Talk:243 Ida/Collaboration

Open issues

• Should Dactyl be merged into this article?
  • I think it probably should. Reyk _YO! 00:50, 27 October 2008 (UTC)
• No references for max/min visual magnitude.
• Should List of geological features on 243 Ida and Dactyl be merged into this article? Perhaps everything else could be merged, leaving only the crater list, and it could be renamed.
• Should we create a draft version of the article? If there is enough new content to be added, it could qualify for a DYK, but the improvements would have to be made to article space all at once. Wronkiew (talk) 06:53, 13 November 2008 (UTC)
• Hi Wronkiew, sorry I've been slack about this lately. Real life has been a pain. I definitely think there's enough material for a 5-fold expansion. I suggest using the bottom of this page as a draft. Reyk _YO! 07:58, 20 November 2008 (UTC)

  I reviewed the DYK requirements again and I don't think that this article will qualify even with a 5-fold expansion. It's just too big to start with. The requirements say that if it exists before the 5 day improvement drive, it has to be a stub or a short article. 8 KB is a bit more than a "short article". Wronkiew (talk) 17:54, 9 December 2008 (UTC)

  I've asked at Wikipedia talk:Did you know how long is too long. If it does turn out that a DYK isn't going to happen, then we can make our changes directly to the article but I don't want to ruin any DYK chance we have by jumping in too early. BTW, I have made a small start at my snadbox (sic). Reyk _YO! 21:34, 9 December 2008 (UTC)

  It doesn't look as though there is a maximum length. Reyk _YO! 00:58, 10 December 2008 (UTC)

• Should we put the Exploration section nearer the start of the article than the end? Most of what is known about Ida comes from the Galileo flyby. It wouldn't make much sense to talk about the composition of Ida and the regolith, inevitably mentioning Galileo results, before talking about the flyby. Reyk _YO! 22:41, 21 November 2008 (UTC)

  Sure. Some of the FAs combine exploration and discovery into a history section. I would prefer to keep discussion about the flyby out of the physical characteristics sections if possible, though. Wronkiew (talk) 04:48, 22 November 2008 (UTC)

  I think we should combine the discovery and exploration section into a single section, because what little material I can find about the discovery won't allow me to write more than a few sentences. Reyk _YO! 03:04, 30 November 2008 (UTC)

• We will need to decide soon on a citation format. My preference is for this one, but I am open to using other formats. Wronkiew (talk) 04:02, 31 December 2008 (UTC)
  • It looks as though we're going to be referring to several of the sources multiple times, so the shortened notes with wikilinks format looks quite sensible. Let's go with that one. Reyk _YO! 04:14, 31 December 2008 (UTC)
• Still very little information regarding the discovery of Ida

  I added two more sources with some information on the discovery. I'll see if I can find more later. Wronkiew (talk) 07:43, 2 January 2009 (UTC)

  Hmm, I can't seem to open either of them. I get "page not found" errors. Can you double-check the URL? PS. I wish I had your genius for digging up sources. Reyk _YO! 07:46, 2 January 2009 (UTC)

  Sorry about that, I should have checked the links. I changed the link to the book description on Google instead. Wronkiew (talk) 01:13, 3 January 2009 (UTC)

Outline

Infobox

Dibs Reyk _YO! 07:36, 25 January 2009 (UTC)

243 Ida

Galileo image of 243 Ida. The tiny dot to the right is its moon, Dactyl.
Discovery
Discovered by	Johann Palisa
Discovery site	Vienna
Discovery date	September 29, 1884
Designations
Alternative designations	A910 CD; 1988 DB1
Minor planet category	Main belt (Koronis)
Orbital characteristics
Epoch JD 2454800.5 (2008-Nov-30.0)
Aphelion	2.991 AU (4.474×1011 m)
Perihelion	2.732 AU (4.087×1011 m)
Semi-major axis	2.862 AU (4.281×1011 m)
Eccentricity	0.0452
Orbital period (sidereal)	1,768.136 days (4.84089 a)
Average orbital speed	0.2036 °/s
Mean anomaly	191.869°
Inclination	1.138°
Longitude of ascending node	324.218°
Argument of perihelion	108.754°
Known satellites	Dactyl
Physical characteristics
Dimensions	53.6 × 24.0 × 15.2 km
Mean radius	15.7 km
Mass	4.2 ± 0.6 ×1016 kg
Mean density	2.6 ± 0.5 g/cm3
Equatorial surface gravity	0.3–1.1 cm/s2
Synodic rotation period	4.63 hours (0.193 d)
North pole right ascension	168.76°
North pole declination	-2.88°
Geometric albedo	0.2383
Temperature	200 K (−73 °C)
Spectral type	S
Absolute magnitude (H)	9.94

• Johann Palisa discovered Ida on September 29, 1884 (Raab 2002)
• Both Ida and moon have a temperature of 200 K (Holm 1994)
• Ida observed bulk density 2600 +/- 500 kg/m^-3 (Wilson, Keil & Love 1999, p. 480)
• Ida belongs to the Koronis family (Holm 1994)
• Ida period is 4.63 hours (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida adopted mean obliquity (ϵ): 156° (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida ecliptic longitude (λ): 263° (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida mass 0.0042 ± 0.0006 ×10¹⁹ kg (Belton et al. 1995) (Britt et al. 2002, p. 486)
• Ida diameter 31.4 km (Belton et al. 1995) (Britt et al. 2002, p. 486)
• Ida bulk density 2.6 ± 0.5 g/cm³ (Belton et al. 1995) (Britt et al. 2002, p. 486)
• Orbital information (JPL 2008)
  • Epoch: 2454800.5 (2008-Nov-30.0)
  • Aphelion: 2.991 AU
  • Perihelion: 2.732 AU
  • Semi-major axis: 2.862 AU
  • Eccentricity: 0.0452
  • Orbital period: 1768.136 d (4.84 y)
  • Mean anomaly: 191.869°
  • Inclination: 1.138°
  • Longitude of ascending node: 324.175°
  • Argument of perihelion: 107.897°
  • Time of perihelion passage: 2455626.273 (2011-Mar-05.773) JED
  • Mean motion: .2036 deg/d
• Absolute magnitude: 9.94 (JPL 2008)
• Geometric albedo: 0.2383 (JPL 2008)
• Alternate Designations: 1988 DB1 = A910 CD (JPL 2008)
• Surface gravity 0.3–1.1cm/s² (Thomas et al. 1996)
• Ida north pole right ascension (α₀): 168.76° (Seidelmann et al. 2007, p. 171)
• Ida north pole declination (δ₀): -2.88° (Seidelmann et al. 2007, p. 171)

Introduction

Dibs Wronkiew (talk) 23:35, 21 February 2009 (UTC)

Discovery and exploration

Discovery

Discoverer

Ida was discovered on September 29, 1884 by Austrian astronomer Johann Palisa at the Vienna Observatory. It was Palisa's 45th asteroid discovery.

• Johann Palisa discovered Ida on September 29, 1884 (Raab 2002)
  • Vienna Observatory
  • Either the 27" or the 12" refractor
• Ida was the 45th asteroid discovered by Palisa (Ridpath 1897, p. 206)

Name

Ida is named after the nymph that raised Zeus in greek mythology.

• Ida is named after the nymph that raised Zeus (NASA 2005)

Observations

• HST observed Ida for 8 hours on 1994-04-26 (Byrnes & D'Amario 1994)
  • Dactyl was less than 700 km from Ida at the time

Exploration

Galileo flyby

Dibs Wronkiew (talk) 05:42, 25 January 2009 (UTC)

• NASA policy to include asteroid flybys when crossing the asteroid belt (D'Amario, Bright & Wolf 1992, p. 26)
• Choice to attempt Ida determined the arrival date of Galileo at Jupiter (D'Amario, Bright & Wolf 1992, p. 26)
• Ida was optional, choice based on available propellant (D'Amario, Bright & Wolf 1992, p. 36)
• Flyby cost 34 kg of propellant (D'Amario, Bright & Wolf 1992, p. 72)
• Galileo flybys the first spacecraft encounters with asteroids (Chapman 1996, p. 699)
• Galileo spacecraft launch (D'Amario, Bright & Wolf 1992, p. 24)
  • Space Shuttle Atlantis
  • 18 October 1989

• Flyby of Ida on 28 August 1993 (D'Amario, Bright & Wolf 1992, p. 36)
• Ida flyby during second crossing through the belt (D'Amario, Bright & Wolf 1992, p. 29)
• Spacecraft velocity compared to Ida was 12.4 km/s (D'Amario, Bright & Wolf 1992, p. 36)
• Galileo closest approach 2400km (NASA 2005)
• Images from SSI at ranges between 240,350 and 2,390 km (Sullivan et al. 1996, p. 120)
• Ida's short rotational period allowed Galileo to image most of the surface (Sullivan et al. 1996, p. 120)
• Galileo observed ~95% of Ida's surface (Thomas et al. 1996)

• Transmission of Ida images was delayed until Galileo was closer to the Earth (Monet et al. 1994, p. 2293)
  • Low bit rate when Galileo is farther away
• Galileo finished transmitting Ida data in June 1994 (Holm 1994)
• Best Ida image had a resolution of about 108 m/pixel (Chapman 1996, p. 705)
• First five images from Ida in September 1993, the rest was transmitted the next spring (Chapman 1996, p. 707)
• Five frame mosaic of Ida at a resolution of 31–38 m/pixel (Chapman et al. 1994, p. 237)
• Galileo sent five high resolution (31-38m/pixel) pictures immediately, remainder in 1994 (Greeley et al. 1994, p. 469)
• Failure of Galileo's main antenna complicated data transmission (Chapman 1994, p. 358)
• Galileo flyby of Ida and Gaspra provided the first high resolution images of asteroid surfaces (Lee et al. 1996, p. 87)

Discoveries

Dibs Wronkiew (talk) 06:50, 25 January 2009 (UTC)

• The field of "asteroid geology" started with Galileo and NEAR probes (Geissler, Petit & Greenberg 1996, p. 57)
• More geological diversity than Gaspra (Chapman et al. 1994, p. 238)
  • Possibly due to larger size
• Dactyl the first confirmed satellite discovered around an asteroid (Chapman 1996, p. 709)
• Galileo flybys provided new insights about the relationship between meteorites and asteroids (Chapman 1996, p. 699)

• Association between asteroid types and meteor types is uncertain (Wilson, Keil & Love 1999, p. 479)
• S-class either ordinary chondrite or stony-iron (Wilson, Keil & Love 1999, p. 479)
  • Chondrite = primitive
  • Stony-iron = differentiated
• Significance of finding Dactyl's orbit (Byrnes & D'Amario 1994)
  • Permitted the determination of Ida's density
  • First time the mass of an S-type asteroid could be found
• Low bulk density rules out a half-metallic composition even if it's a rubble pile (Chapman 1995, p. 496)

• Ida demonstrates the space weathering process (Chapman 1996, p. 710)
• Space weathered material becomes redder as it ages (Chapman 1996, p. 710)
• Space weathering is a superficial process (Chapman 1996, p. 700)
• Space weathering affects the appearance of Ida's surface over time (Chapman 1996, p. 700)
• Spectrum indicates Space weathering prominent on Ida (Chapman 1995, p. 496)
  • Not as prominent on Dactyl
• Taking weathering into account resolves the differences between S-type asteroids and OCs (Chapman 1996, p. 699)

• S-type asteroids are the most common in the inner part of the main asteroid belt (Chapman 1996, p. 699)
• OC meteorites are the most common type found on the Earth's surface (Chapman 1996, p. 699)
• Ida and Dactyl may share the mineral composition of OC meteorites (Chapman 1996, p. 700)
• Extrapolating spectra of weathered regions on Ida, to less weathered regions, to Dactyl indicates ordinary chondritic (OC) composition (Chapman 1995, p. 496)
  • Ida and other Koronis asteroids may be the source of OC meteorites

Physical characteristics

• Both Ida and moon have a temperature of 200 K (Holm 1994)

Mass and size

Mass

Dibs Wronkiew (talk) 06:56, 31 January 2009 (UTC)

• Mass is 3.65–4.99 x 10¹⁶ kg (Petit et al. 1997, pp. 179–180)
  • Inferred from the long term stability of its moon
• Ida mass 0.0042 ± 0.0006 ×10¹⁹ kg (Belton et al. 1995) (Britt et al. 2002, p. 486)
• Escape velocity from Ida is 20 m/s (Lee et al. 1996, p. 99)
• Surface gravity 0.3–1.1cm/s² (Thomas et al. 1996)

Size

• Best fit ellipsoid 59.8 x 25.4 x 18.6 km (Chapman 1996, p. 707)
• Ida's volume 16,100 ± 1900 km³ (Chapman 1996, p. 709)
• Ida diameter 31.4 km (Belton et al. 1995) (Britt et al. 2002, p. 486)
• Ida's volume determined by Galileo to within 12% (Britt et al. 2002, p. 489)

Shape

Dibs. Reyk _YO! 01:57, 26 January 2009 (UTC)

Ida is a distinctly elongated asteroid, with an irregular surface, and is somewhat "croissant-shaped". The elongation of the best-fit triaxial ellipsoid is 2.35, and the asteroid possesses a "waist" that separates it into two geologically dissimilar halves. This constricted shape is consistent with Ida being made of two large, solid components with loose debris filling the gap between them, but the constriction was imaged by Galileo in high resolution and no such loose material was seen. There are steep slopes, up to about 50°, present on Ida but few areas where the slope exceeds 35°.

Ida's irregular shape is, together with its low surface gravity and fast rotation, responsible for the asteroid's highly uneven gravitational field. The surface gravity is lowest at the ends of the asteroid, due to the fast rotation, and near the minimum radius due to less mass being present interior to that location.

• Elongation of Ida 2.35 (Geissler, Petit & Greenberg 1996, p. 58)
• Ida "croissant-shaped" (Chapman 1996, p. 707)
• "Waist" around the asteroid separating two geologically dissimilar halves (Chapman 1996, p. 707)
• Ida's constricted shape is consistent with it being made of two large components with loose material filling the gap between them (Thomas & Prockter 2004)
  • However, the constriction was imaged in high resolution and does not display any such loose debris
• Ida is elongated in shape (Bottke et al. 2002, p. 10)
  • Irregular surface
• Ida's irregular gravitational field due to low surface gravity, fast rotation and irregular shape (Cowen 1995)
• Surface gravity lowest at the ends and middle (Thomas et al. 1996)
  • low at ends because of rotation
  • low in middle because little mass interior to location
• Maximum slopes about 50°, but few areas with slopes of more than 35° (Thomas et al. 1996)
• Ida ephemeris position of the prime meridian at J2000 (W): 265.95° + 1864.6280070d (Seidelmann et al. 2007, p. 171)

Surface features

Dibs Wronkiew (talk) 07:49, 20 February 2009 (UTC)

Regolith

Dibs Wronkiew (talk) 05:10, 26 January 2009 (UTC)

• Ida regolith 50–100 m thick (Chapman 1996, p. 707)
• Movement of debris downslope on Ida suggests the presence of regolith (Greeley et al. 1994, p. 470)
• Blocks indicate the presence of regolith (Lee et al. 1996, p. 88)
• Upper limit for Ida regolith depth is 130 m (Lee et al. 1996, p. 96)

• Ida's surface is mostly olivine with small amounts of orthopyroxene (Holm 1994)
• Ida shows color variations across its surface (Chapman 1996, p. 710)
  • Fresh craters are less red than the rest of the surface
  • Similar colors from the ejecta of the fresh crater Azzurra
• NOTE: "Earlier premature reports by NIMS investigators that Ida is an exceptionally olivine-rich object (Carlson, 1994) and that Dactyl is rich in clinopyroxene (Carlson et al., 1994) have been effectively withdrawn (J. Granahan, pers. comm., 1995; R. Carlson [pers. comm., 1996] agrees that the evidence for clinopyroxene is 'weak')." (Chapman 1996, p. 714)
• Pyroxene and olivine are silicate minerals (Chapman 1996, p. 701)
• Spectrum indicates Space weathering prominent on Ida (Chapman 1995, p. 496)

Structures

Dibs Wronkiew (talk) 22:01, 14 February 2009 (UTC)

• "Waist" around the asteroid separating two geologically dissimilar halves (Chapman 1996, p. 707)
• Differences between the two halves might be spurious (Stooke 1997, p. 1385)
• "waist" might be composed of overlapping craters rather than structural (Stooke 1997, p. 1385)

• Linear structure on the surface named Townsend Dorsum (Sárneczky & Kereszturi 2002)
  • Covers 150 degrees of arc
  • ~40 km long
  • Not visible during closest approach by Galileo
• Ida Region 1 has a prominent ridge (Chapman 1996, p. 707)
• 40 km long ridge (Chapman 1996, p. 707)
• The morphology of Townsend Dorsum suggests displacement along a fault line (Thomas & Prockter 2004)
  • However, the projection of the ridge into higher resolution area does not show fault topography
  • Possibly an older feature like a compositional discontinuity
• Ida Region 1 contains a large indentation Vienna Regio (Chapman 1996, p. 707)

Craters

Dibs. Reyk _YO! 06:26, 25 January 2009 (UTC)

Ida is one of the most densely cratered bodies in the Solar System, and impacts have been the primary process shaping its surface. Ida's surface is covered with craters of all sizes and stages of degradation, and range in age from fresh to very old. Some of Ida's craters may have been formed during the breakup of the Koronis family parent body. The largest crater is 12 kilometres (7.5 mi) across. The craters are not distributed evenly over Ida's surface. Region 2 contains nearly all of the large (>6 kilometres (3.7 mi)) craters but Region 1 has no large craters at all. Chains of craters are also apparent.

The craters on Ida are simple in structure. They are bowl-shaped with no flat bottoms and no central peaks, with the exception of Fingal, a fresh, asymmetric crater that has a sharp boundary between the crater floor and wall on one side. The ejecta excavated by impacts is, like on many asteroids, deposited differently on Ida than on planets because of its rapid rotation, low gravity and irregular shape. Ejecta blankets that settle around craters are asymmetrical and material that escapes from the asteroid is permanently lost.

The Azzurra basin seems to be the most recent major impact on Ida. The ejecta from this collision is distributed discontinuously over Ida and is responsible for the large-scale color and albedo variations across the asteroid's surface. The protrusion north of crater Choukoutien is smoother and less cratered than the rest of Ida. The 0° meridian on Ida is defined to pass through the crater Afon.

• Ida meridian goes through Afon crater (Seidelmann et al. 2007, p. 171)

• Impacts are the dominant process shaping the surface of Ida (Geissler, Petit & Greenberg 1996, pp. 57–58)
• Deposition of ejecta is different on asteroids than on planets because of rapid spin, odd shapes, low gravity (Geissler, Petit & Greenberg 1996, p. 58)
• Escaped ejecta from main belt asteroids is permanently lost (Geissler, Petit & Greenberg 1996, p. 58)
• Ida Region 2 contains nearly all of the large (>6 km) craters (Chapman 1996, p. 707)
• Ida Region 1 has no large craters (Chapman 1996, p. 707)
• Ida has a full range of craters, from fresh to very old (Chapman 1996, p. 707)
• The rapid rotation and low gravity of Ida produces asymmetrical ejecta blankets around craters (Geissler et al. 1996, p. 155)
• One of the most densely cratered objects in the Solar System (Chapman et al. 1994, p. 237)
• Chains of craters are apparent (Greeley et al. 1994, p. 469)
• Simple craters only, bowl shaped, no flat bottoms, no central peaks (Sullivan et al. 1996, p. 124)
  • Except for Fingal, which is fresh, asymmetric, and has a sharp boundary between the floor and wall on one side
• Surface covered in craters of all sizes and stages of degradation (Chapman 1994, p. 363)
• One of the most densely cratered bodies in the solar system (Chapman 1994, p. 363)
• Ida's crater Azzurra (Chapman 1996, p. 710)
  • Ejecta deposited discontinuously around Ida
• Azzurra basin appears to be the most recent major impact (Geissler et al. 1996, p. 141)
• Large-scale color and albedo variation across Ida's surface is associated with Azzurra Crater (Bottke et al. 2002, p. 9)
• Ida's largest crater is 12 km (Bottke et al. 2002, p. 10)
• Protrusion north of crater Choukoutien is smoother and less cratered than the rest of Ida (Sullivan et al. 1996, p. 128)
• Some of Ida's craters may be from the breakup of the Koronis parent body (Chapman 1995, p. 496)

Ejecta blocks

Dibs Wronkiew (talk) 02:01, 11 February 2009 (UTC)

• Ida has about 20 large ejecta blocks, up to 150 m across (Chapman 1996, p. 707)
• Most 40–150 m ejecta blocks in a cluster on one side of Ida near Mammoth and Lascaux (Geissler et al. 1996, p. 141)
• Impact blocks are the largest debris particles on the surface (Sullivan et al. 1996, p. 132)
• Ida's irregular gravitational field due to low surface gravity, fast rotation and irregular shape (Cowen 1995)
  • May explain placement of ejecta blocks
• Ejecta blocks rapidly broken down by other impacts (Cowen 1995)
  • Those present must be fairly young
• Azzurra is on the trailing rotational edge of the asteroid opposite the ejecta blocks (Cowen 1995)
• Azzurra contains a smaller, 3km, crater in its eastern rim (Stooke 1997, p. 1385)
  • this smaller crater might be the source of the ejecta rather than Azzurra itself
• Blocks indicate the presence of regolith (Lee et al. 1996, p. 88)
• The two largest blocks on Ida are about half as tall as they are wide (Lee et al. 1996, p. 88)
• The blocks are probably fragments of Ida ejected in an impact (Lee et al. 1996, p. 96)
• Blocks could be leftover fragments from the parent body (Lee et al. 1996, p. 97)
• Most blocks are located in Ida craters Lascaux and Mammoth (Lee et al. 1996, p. 97)

Grooves

Dibs Wronkiew (talk) 06:03, 19 February 2009 (UTC)

• Ida Region 2 contains all the grooves (Chapman 1996, p. 707)
• Ida's grooves are concentrated in three areas but are not obviously related to individual craters or structures. (Thomas & Prockter 2004)
  • One set of grooves is opposite Vienna Regio. Possibly caused by that impact and "reactivated" by later impacts such as Azzurra.
  • If grooves are the result of focussed seismic waves, Ida is probably not a rubble pile
• Grooves up to 4 km long, 350 m depth, usually 100 m deep (Sullivan et al. 1996, p. 131)
• Ida grooves near Mammoth, Lascaux, and Kartchner (Sullivan et al. 1996, p. 132)
• Grooves indicate internal fractures (Sullivan et al. 1996, p. 136)
• Computer simulations of impacts on Ida reproduce the grooves if the interior is homogeneous (Asphaug, Ryan & Zuber 2003, p. 475)

Composition

Classification and mineral content

Dibs Wronkiew (talk) 06:29, 26 January 2009 (UTC)

• Ida is S-class (Wilson, Keil & Love 1999, p. 479)
• Ida is S{IV} class (Chapman 1996, p. 704)
• Association between asteroid types and meteor types is uncertain (Wilson, Keil & Love 1999, p. 479)
• S-class either ordinary chondrite or stony-iron (Wilson, Keil & Love 1999, p. 479)
  • Chondrite = primitive
  • Stony-iron = differentiated
• Ida's surface is mostly olivine with small amounts of orthopyroxene (Holm 1994)
• NOTE: "Earlier premature reports by NIMS investigators that Ida is an exceptionally olivine-rich object (Carlson, 1994) and that Dactyl is rich in clinopyroxene (Carlson et al., 1994) have been effectively withdrawn (J. Granahan, pers. comm., 1995; R. Carlson [pers. comm., 1996] agrees that the evidence for clinopyroxene is 'weak')." (Chapman 1996, p. 714)
• Pyroxene and olivine are silicate minerals (Chapman 1996, p. 701)
• No large variations in mineral content across the surface (Sullivan et al. 1996, p. 135)
• Extrapolating spectra of weathered regions on Ida, to less weathered regions, to Dactyl indicates ordinary chondritic (OC) composition (Chapman 1995, p. 496)
• Low bulk density rules out a half-metallic composition even if it's a rubble pile (Chapman 1995, p. 496)
• Ordinary chondrites contain varying amounts of olivine, pyroxene, iron, and feldspar (Lewis 1996, p. 89

  The chondrites fall naturally into five composition classes, of which three have very similar mineral contents, but different proportions of metal and silicates. All three contain abundant iron in three different forms (ferrous iron oxide in silicates, metallic iron, and ferrous sulfide), usually with all three abundant enough to be classified as potential ores. all three contain feldspar (an aluminosilicate of calcium, sodium, and potassium), pyroxene (silicates with one silicon atom for each atom of magnesium, iron, or calcium), olivine (silicates with two iron or magnesium atoms per silicon atom), metallic iron, and iron sulfide (the mineral triolite). These three classes, referred to collectively as the ordinary chondrites, contain quite different amounts of metal.

  )
• If Ida is assumed to be of homogeneous density then maximum moment of inertia coincides with spin axis. This suggests no regions of differing density. (Thomas & Prockter 2004)

Porosity

Dibs Wronkiew (talk) 22:59, 25 January 2009 (UTC)

• Calculated density of Ida assumes chondrite (Wilson, Keil & Love 1999, p. 479)
• Ida inferred grain density 3480–3640 kg/m³ (Wilson, Keil & Love 1999, p. 480)
  • Based on chondrite classification
• Ida observed bulk density 2600 ± 500 kg/m³ (Wilson, Keil & Love 1999, p. 480)
• Density of Ida directly measured by spacecraft (Wilson, Keil & Love 1999, p. 482)
• Density is 2.27–3.10 g/cm³ (Petit et al. 1997, p. 182)
• Ida bulk density 2.6 ± 0.5 g/cm³ (Belton et al. 1995) (Britt et al. 2002, p. 486)
• If Ida is assumed to be of homogeneous density then maximum moment of inertia coincides with spin axis. This suggests no regions of differing density. (Thomas & Prockter 2004)
• Porosity of Ida 11–42% (Wilson, Keil & Love 1999, p. 480)

• Debris layer at least 50 m thick, corresponding to the upper layer of megaregolith (Sullivan et al. 1996, p. 135)
• Megaregolith depth ranges from hundreds of meters to a few kilometers (Sullivan et al. 1996, p. 135)
• Megaregolith under Mammoth, Lascaux, and Undara may go all the way to the core (Sullivan et al. 1996, p. 135)

Orbit and rotation

Asteroid family

Dibs. Reyk _YO! 00:53, 26 January 2009 (UTC)

Ida is a member of the Koronis family, a group of asteroids with similar orbits. The Koronis family was recognized as a family by Kiyotsugu Hirayama, who proposed in 1918 that the group was the remnants of a destroyed precursor body. The parent body was probably about 120 kilometres (75 mi) in diameter.

• Ida belongs to the Koronis family (Holm 1994)
• Koronis family has similar orbits (Chapman 1996, p. 700)
  • Hirayama recognized the family, in 1918 proposed that it comprised remnants of a precursor body
• Some of Ida's craters may be from the breakup of the Koronis parent body (Chapman 1995, p. 496)
• Koronis parent body was about 120 km diameter (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)

Spin

Ida's rotation period is 4.63 hours, making it one of the fastest rotating known asteroids. It is in the top 10% of measured asteroids by spin. Ida's spin axis coincides with its maximum moment of inertia, if its density is assumed to be even throughout. This suggests that there are no major variations of density within the asteroid.

• Rotation period of Ida is 4.63 hours (Geissler, Petit & Greenberg 1996, p. 58)
• Ida has a rotation period of 4.63 hr (Greenberg et al. 1996, p. 107)
  • One of the fastest rotating known asteroids
• If Ida is assumed to be of homogeneous density then maximum moment of inertia coincides with spin axis. This suggests no regions of differing density. (Thomas & Prockter 2004)
• Ida period is 4.63 hours (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida in the top 10% of measured asteroids by spin (Geissler, Petit & Greenberg 1996, p. 58)
• Ida's spin is in the top 10% of measured asteroids (Lagerkvist et al. 1989) (Geissler et al. 1996, p. 141)

Coordinates of north pole

• Ida adopted mean obliquity (ϵ): 156° (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida ecliptic longitude (λ): 263° (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)

Origin

Dibs Wronkiew (talk) 00:00, 1 February 2009 (UTC)

• Analysis of cratering gives two age ranges, 50 million years, or more than 1 billion (Greenberg et al. 1996, p. 117)
• Ida is billions of years old (Bottke et al. 2002, p. 10)
• Two different ages for Ida and Dactyl (Hurford & Greenberg 2000, p. 1595)
  • Ida is about a billion years old
  • Dactyl should have decayed in less than 100 million years
• Ida may be ten times older than Gaspra (Chapman 1994, p. 363)
• An event formed the Koronis family 1.5 billion years ago (Petit et al. 1997, p. 182)
• Ida "formed and evolved under the overwhelming influence of collisional processes" (Greenberg et al. 1996, p. 106)
• Asteroid families are created from "catastrophic disruption events" (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Koronis parent body was about 120 km diameter (Vokrouhlicky, Nesvorny & Bottke 2003, p. 147)
• Ida and Dactyl believed to have originated in the disruption of the parent body about a billion years ago (Lee et al. 1996, p. 97)
• Koronis parent was partially differentiated (Greenberg et al. 1996, p. 117)
• Ida does not contain core material from parent (Greenberg et al. 1996, p. 117)

Moon

Dibs. Wronkiew (talk) 17:09, 26 February 2009 (UTC)

Discovery

Dibs. Reyk _YO! 02:19, 26 January 2009 (UTC)

Ida has a small moon, Dactyl, the first satellite of an asteroid to be discovered. It was found on February 17, 1994 by Galileo mission member Ann Harch, while examining the delayed image downloads. Galileo recorded 47 images of Dactyl over an observation period of 5 1/2 hours in August 1993. The spacecraft was 10,760 kilometres (6,690 mi) from Ida and 10,870 kilometres (6,750 mi) from Dactyl when the first image was taken, 14 minutes before Galileo made its closest approach to Ida.

Dactyl's original designation was 1993 (243) 1. It was renamed by the International Astronomical Union in 1994, after the mythological dactyls who inhabited Mount Ida.

• 5 1/2 hours of observations of Dactyl (Petit et al. 1997, p. 177)
• 47 images of Dactyl (Petit et al. 1997, p. 177)
• Ann Harch of the Galileo camera team first discovered Ida's moon (Holm 1994)
  • Images processed on February 17, 1994
• Dactyl the first confirmed satellite discovered around an asteroid (Chapman 1996, p. 709)
• First image of Dactyl taken at a distance of 10,870km from Dactyl, 14 minutes before Galileo's closest approach to Ida (Mason 1994, p. 108)
• IAU named Dactyl in 1994 (Green 1994)
• Previous designation was 1993 (243) 1 (Green 1994)
• Dactyl found in 1994-02 from data recorded in 1993-08 (Belton & Carlson 1994)
• Spacecraft was 10,760 km from Ida when first pictures were taken (Belton & Carlson 1994)
• Initial designation 1993 (243) 1 (Belton & Carlson 1994)
• "These things then are as I have described them. As for the Olympic games, the most learned antiquaries of Elis say that Cronus was the first king of heaven, and that in his honor a temple was built in Olympia by the men of that age, who were named the Golden Race. When Zeus was born, Rhea entrusted the guardianship of her son to the Dactyls of Ida, who are the same as those called Curetes. They came from Cretan Ida – Heracles, Paeonaeus, Epimedes, Iasius and Idas." (Pausanias & 5.7.6)

Physical characteristics

• Dibs. Reyk _YO! 23:10, 6 February 2009 (UTC)

Dactyl is an "egg-shaped" object measuring 1.6 × 1.4 × 1.2 km. It is oriented with its longest axis pointing towards Ida. Like Ida, Dactyl exhibits saturation cratering. There are more than a dozen craters with a diameter greater than 80 metres (260 ft) on Dactyl's surface, indicating that the moon has suffered many collisions during its history. About six of the easily identifiable craters on Dactyl are in a linear chain, suggesting a local origin such as material ejected from Ida. Unlike the craters on Ida, there are indications that Dactyl's craters possess central peaks. These central peaks, and Dactyl's spheroidal shape, imply that, despite its low gravity, Dactyl is gravitationally controlled.

Dactyl has an escape velocity of about 0.5 metres per second (1.6 ft/s) and, like Ida, a temperature of 200K.

• Dactyl about 1.5 km long (Holm 1994)
• Both Ida and moon have a temperature of 200 K (Holm 1994)
• 1.6 x 1.4 x 1.2 km (Chapman 1996, p. 709)
• Egg shaped (Chapman 1996, p. 709)
• Oriented with its longest axis pointing towards Ida (Chapman 1996, p. 709)
• Saturation cratering (Chapman 1996, p. 709)
• About six craters form a linear chain (Chapman 1996, p. 709)
• Dactyl has more than a dozen craters greater than 80m in diameter (NASA 2005)
  • Indicates many collisions during its history
• Dactyl appears to have craters with central peaks (Asphaug, Ryan & Zuber 2003, p. 463)
• Despite its low gravity, Dactyl seems to be gravitationally controlled (Asphaug, Ryan & Zuber 2003, p. 463)
• Escape velocity is half a meter per second

Composition

Dactyl's surface was initially thought to be composed of equal parts clinopyroxene and the silicate minerals olivine and orthopyroxene and clinopyroxene but later studies indicate that the evidence for clinopyroxene is "weak".

• Dactyl's surface is equal parts olivine, orthopyroxene, and clinopyroxene (Holm 1994)
• NOTE: "Earlier premature reports by NIMS investigators that Ida is an exceptionally olivine-rich object (Carlson, 1994) and that Dactyl is rich in clinopyroxene (Carlson et al., 1994) have been effectively withdrawn (J. Granahan, pers. comm., 1995; R. Carlson [pers. comm., 1996] agrees that the evidence for clinopyroxene is 'weak')." (Chapman 1996, p. 714)
• Pyroxene and olivine are silicate minerals (Chapman 1996, p. 701)

Mass

• "An astronaut would need to exercise care in order to walk on the surface of Dactyl, as an overly energetic step would lead to permanent departure" (Geissler et al. 1996, p. 142)

Comparison with Ida

• Dactyl's albedo and spectrum not very different from Ida's (Chapman et al. 1994, p. 455)
• Ida and Dactyl have similar compositions (Bottke et al. 2002, p. 10)
• Spectrum indicates Space weathering prominent on Ida (Chapman 1995, p. 496)
  • Not as prominent on Dactyl
• Dactyl thought to have less regolith than Ida (Chapman 1995, p. 496)
• Dactyl 10-20 times smaller than Ida (Belton & Carlson 1994)

Orbit and rotation

• Dibs. Reyk _YO! 21:02, 15 February 2009 (UTC)

Dactyl's orbit around Ida is not known with great precision. Galileo was in the plane of Dactyl's orbit when most of the images of the moon were taken, which made determining its exact orbit difficult. It is known that Dactyl orbits in the prograde direction and is inclined about 8° to Ida's equator. Based on computer simulations Dactyl's pericenter must be more than about 65 kilometres (40 mi) from Ida if it is to remain in a stable orbit. The range of orbits generated by the computer simulations was narrowed down by the necessity of having the simulated orbits pass through points at which Galileo observed Dactyl to be, particularly a reference point approximately 90 kilometres (56 mi) from Ida at longitude 85° taken at 16:52:05 UT on 1993-08-28. On 1994-04-26, the Hubble Space Telescope observed Ida for eight hours and was unable to spot Dactyl. It would have been able to spot the moon if it was more than about 700 kilometres (430 mi) from Ida.

Dactyl's orbital period is approximately 20 hours, assuming the moon is in a circular orbit around Ida. Its orbital speed is about 10 metres per second (33 ft/s), "about the speed of a fast run or a slowly thrown baseball". The moon's longest axis points toward Ida.

• Dactyl's orbit is prograde (Petit et al. 1997, p. 179)
• At 16:52:05 UT on 1993-08-28, Dactyl was 90 km from Ida at longitude 85 deg (Petit et al. 1997, p. 188)
• Dactyl pericenter greater than 65 km (Petit et al. 1997, p. 195)
• Search for Dactyl by Hubble turned up nothing (Belton et al. 1995) (Petit et al. 1997, p. 177)
• Galileo was in the plane of Dactyl's orbit for most of the photos of Dactyl (Byrnes & D'Amario 1994)
  • This made determining the orbit difficult
• Dactyl's orbital speed is about 10 m/s "about the speed of a fast run or a slowly thrown baseball" (Byrnes & D'Amario 1994)
• HST observed Ida for 8 hours on 1994-04-26 (Byrnes & D'Amario 1994)
  • Dactyl was less than 700 km from Ida at the time
• Longest axis pointing towards Ida (Chapman 1996, p. 709)
• Period of Dactyl's orbit is approx. 20 hours, assuming circular orbit (Chapman et al. 1994, p. 455)
• Dactyl's orbit is inclined about 8° to Ida's equator (Petit et al. 1997, p. 177

Age & Origin

Dactyl is believed to have originated from the same parent body as Ida, from the disruption of the parent of the Koronis asteroid family, but it is possible that it formed formed more recently, perhaps as ejecta from a large impact on the asteroid. It is extremely unlikely that it was captured by Ida. There is evidence that it suffered a major impact around 100 million years ago, which reduced its size.

• Dactyl probably created at the same time as Ida (Durda 1996) (Petit et al. 1997, p. 182)
• Possible Dactyl was formed more recently (Durda & Geissler 1996) (Petit et al. 1997, p. 182)
• Dactyl may have been impacted around 100 million years ago (Greenberg et al. 1996, p. 117)
  • Size reduction
• Ida and Dactyl from the same parent body (Greenberg et al. 1996, p. 116)
• Differences in composition between Ida and Dactyl indicate differentiation in the parent body (Greenberg et al. 1996, p. 116)
• Dactyl has more than a dozen craters greater than 80m in diamter (NASA 2005)
  • Indicates many collisions during its history
• Virtually impossible for Dactyl to have been captured by Ida (Mason 1994, p. 108)
• Ida and Dactyl believed to have originated in the disruption of the parent body about a billion years ago (Lee et al. 1996, p. 97)

Model articles

• Ceres
  • Article about a similar object
• Pluto
  • Mostly airless rock with moons
• Mercury
  • Airless rock visited by spacecraft
• Enceladus
  • Airless rock visited by spacecraft, lots of good diagrams
• Craters of the Moon National Monument and Preserve
  • Less similar, but an interesting comparison
• Antarctica
  • For comparison
• Callisto (moon)
  • Another object that features saturation cratering

Notes

Sárneczky, K (2002). "'Global' Tectonism on Asteroids?" (PDF). 33rd Annual Lunar and Planetary Science Conference. Bibcode:2002LPI....33.1381S. Retrieved 2008-10-22. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Wilson, Lionel (1999). "The internal structures and densities of asteroids" (PDF). Meteoritics & Planetary Science. 34 (3): 479–483. Bibcode:1999M&PS...34..479W. Retrieved 2008-10-22. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Geissler, Paul E. (1996). "Ejecta Reaccretion on Rapidly Rotating Asteroids: Implications for 243 Ida and 433 Eros" (PDF). Completing the Inventory of the Solar System. 107. Astronomical Society of the Pacific: 57–67. Bibcode:1996ASPC..107...57G. Retrieved 2008-10-22. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

D'Amario, Louis A. (1992). "Galileo trajectory design" (PDF). Space Science Reviews. 60: 23–78. Bibcode:1992SSRv...60...23D. Retrieved 2008-10-22. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Petit, Jean-Marc (1997). "The Long-Term Dynamics of Dactyl's Orbit" (PDF). Icarus. 130 (1): 177–197. Bibcode:1997Icar..130..177P. doi:10.1006/icar.1997.5788. Retrieved 2008-10-25. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Monet, A. K. B. (1994). "Astrometry for the Galileo mission. 1: Asteroid encounters" (PDF). The Astronomical Journal. 107 (6): 2290–2294. Bibcode:1994AJ....107.2290M. doi:10.1086/117036. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Holm, Jeanne (1994). "Discovery of Ida's Moon Indicates Possible "Families" of Asteroids". The Galileo Messenger (34). NASA. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Byrnes, Dennis V. (1994). "Solving for Dactyl's Orbit and Ida's Density". The Galileo Messenger (35). NASA. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Chapman, Clark R. (1996). "S-Type Asteroids, Ordinary Chondrites, and Space Weathering: The Evidence from Galileo's Fly-bys of Gaspra and Ida" (PDF). Meteoritics. 31: 699–725. Bibcode:1996M&PS...31..699C. Retrieved 2008-10-27. {{cite journal}}: Unknown parameter |month= ignored (help)

Greenberg, Richard (1996). "Collisional and Dynamical History of Ida" (PDF). Icarus. 120 (1): 106–118. Bibcode:1996Icar..120..106G. doi:10.1006/icar.1996.0040. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Geissler, Paul E. (1996). "Erosion and Ejecta Reaccretion on 243 Ida and Its Moon" (PDF). Icarus. 120 (1): 140–157. Bibcode:1996Icar..120..140G. doi:10.1006/icar.1996.0042. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Chapman, Clark R. (1994). "First Galileo image of asteroid 243 Ida" (PDF). Abstracts of the 25th Lunar and Planetary Science Conference. Lunar and Planetary Institute: 237–238. Bibcode:1994LPI....25..237C. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Thomas, Peter C. (2004-05-28). "Tectonics of Small Bodies". Planetary Tectonics. Cambridge Planetary Science. Vol. 11. Cambridge University Press. ISBN 9780521765732. {{cite book}}: |access-date= requires |url= (help); Check date values in: |date= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

Raab, Herbert (2002). "Johann Palisa, the most successful visual discoverer of asteroids" (PDF). Meeting on Asteroids and Comets in Europe. Retrieved 2008-10-23.

"Images of Asteroids Ida & Dactyl". NASA. 2005-08-23. Retrieved 2008-12-04. {{cite web}}: Check date values in: |date= (help)

Bottke, William F., Jr. (2002). "An Overview of the Asteroids: The Asteroids III Perspective" (PDF). Asteroids III. University of Arizona: 3–15. Bibcode:2002aste.conf....3B. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: multiple names: authors list (link)

Vokrouhlicky, David (2003-09-11). "The vector alignments of asteroid spins by thermal torques" (PDF). Nature. 425 (6954): 147–151. Bibcode:2003Natur.425..147V. doi:10.1038/nature01948. Retrieved 2008-10-23. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

Hurford, Terry A. (2000). "Tidal Evolution by Elongated Primaries: Implications for the Ida/Dactyl System" (PDF). Geophysical Research Letters. 27 (11): 1595–1598. Bibcode:2000GeoRL..27.1595H. doi:10.1029/1999GL010956. Retrieved 2008-10-25. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Greeley, R. (1994). "Morphology and Geology of Asteroid Ida: Preliminary Galileo Imaging Observations" (PDF). Abstracts of the 25th Lunar and Planetary Science Conference. Lunar and Planetary Institute: 469–470. Bibcode:1994LPI....25..469G. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Chapman, Clark R. (1996). "Cratering on Ida". Icarus. 120 (1): 77–86. Bibcode:1996Icar..120...77C. doi:10.1006/icar.1996.0038. Retrieved 2008-10-27. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Preprint

• Ida is the second asteroid where craters have been imaged (Chapman et al. 1996)
• Ida is divided into two regions (Chapman et al. 1996)
  • Region 1 is less heavily cratered
  • Region 2 is more cratered
• Dactyl is also saturated with craters (Chapman et al. 1996)
• Crater saturation (Chapman et al. 1996)
• Two processes affect Ida's surface, erosion and regolith production/redistribution
  • Regolith production is dominant because of Ida's mass
• Koronis is "one of the three most populous and well-defined families in the asteroid belt" (Chapman et al. 1996)
• Population of impactors on Ida are similar to that for the Moon (Chapman et al. 1996)

Sullivan, Robert J. (1996). "Geology of 243 Ida" (PDF). Icarus. 120 (1): 119–139. Bibcode:1996Icar..120..119S. doi:10.1006/icar.1996.0041. Retrieved 2008-10-27. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Cowen, Ron (1995-04-01). "Idiosyncrasies of Ida—asteroid 243 Ida's irregular gravitational field". Science News. Retrieved 2008-10-27. {{cite news}}: Check date values in: |date= (help)

Mason, John W. (1994). "Ida's new moon" (PDF). Journal of the British Astronomical Association. 104 (3): 108. Bibcode:1994JBAA..104..108M. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |month= ignored (help)

Chapman, Clark R. (1994). "Asteroid 243 IDA and its satellite" (PDF). Meteoritics. 29: 455. Bibcode:1994Metic..29..455C. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Ridpath, John Clark (1897). The Standard American Encyclopedia of Arts, Sciences, History, Biography, Geography, Statistics, and General Knowledge. Encyclopedia Publishing.

Britt, D. T. (2002). "Asteroid Density, Porosity, and Structure" (PDF). Asteroids III. University of Arizona: 485–500. Bibcode:2002aste.conf..485B. Retrieved 2008-10-27. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Chapman, Clark R. (1994). "The Galileo Encounters with Gaspra and Ida" (PDF). Asteroids, Comets, Meteors: 357–365. Bibcode:1994IAUS..160..357C. Retrieved 2008-10-27.

Chapman, Clark R. (1995). "Galileo Observations of Gaspra, Ida, and Dactyl: Implications for Meteoritics" (PDF). Meteoritics. 30 (5): 496. Bibcode:1995Metic..30R.496C. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |month= ignored (help)

Stooke, P. J. (1997). "Reflections on the Geology of 243 Ida" (PDF). Lunar and Planetary Science XXVIII: 1385–1386. Retrieved 2008-11-29.

Asphaug, Erik (2003). "Asteroid Interiors" (PDF). Asteroids. III. Tucson: Univ. Ariz. Press: 463–484. Retrieved 2009-01-04. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Lee, Pascal (1996). "Ejecta Blocks on 243 Ida and on Other Asteroids" (PDF). Icarus. 120 (1): 87–105. Bibcode:1996Icar..120...87L. doi:10.1006/icar.1996.0039. Retrieved 2008-10-27. {{cite journal}}: Cite has empty unknown parameter: |1= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

"JPL Small-Body Database Browser: 243 Ida". Jet Propulsion Laboratory. 2008-08-25.

Thomas, Peter C. (1996). "The shape of Ida". Icarus. 120 (1): 20–32. Bibcode:1996Icar..120...20T. doi:10.1006/icar.1996.0033. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Seidelmann, P. Kenneth (2007). "Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006" (PDF). Celestial Mechanics and Dynamical Astronomy. 98 (3): 155–180. doi:10.1007/s10569-007-9072-y. Retrieved 2009-01-12. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Green, Daniel W. E. (1994-09-26). "1993 (243) 1 = (243) Ida I (Dactyl)". IAU Circular (6082). International Astronomical Union. Bibcode:1994IAUC.6082....2G.

Belton, Michael J. S. (1994-03-12). "1993 (243) 1". IAU Circular (5948). International Astronomical Union. Bibcode:1994IAUC.5948....2B. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Pausanias (1916). Description of Greece. Translated by Jones, W. H. S. & Omerod, H. A. Loeb Classical Library. ISBN 0674991044.

Lewis, John S. (1996). Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Reading, MA: Addison-Wesley. ISBN 0201479591.

Krasinskya, G. A. (2002). "Hidden Mass in the Asteroid Belt". Icarus. 158 (1): 98–105. Bibcode:2002Icar..158...98K. doi:10.1006/icar.2002.6837. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Unused source citations

List of citations for potentially useful source material:

• Hilton, James L. (2007-11-16). "Masses of the Largest Asteroids". U.S. Naval Observatory. Retrieved 2008-10-23. {{cite web}}: Check date values in: |date= (help)

  Replaced by Petit 1997

• Lee, P. (1994). "Mapping Regolith and Blocks on Asteroid 243 Ida: The Effects of Photometric Viewing Geometry" (PDF). Abstracts of the 25th Lunar and Planetary Science Conference. Lunar and Planetary Institute: 787–788. Bibcode:1994LPI....25..787L. Retrieved 2008-10-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
• Belton, Michael J. S. (1995). "The bulk density of asteroid 243 Ida from Dactyl's orbit". Nature. 374: 785–788. Bibcode:1995Natur.374..785B. doi:10.1038/374785a0. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Preprint (PS).

  The preprint is probably not a reliable source.

• Chapman, Clark R. (1995). "Discovery and Physical Properties of Dactyl a Satellite of Asteroid 243 Ida". Nature. 374 (6525): 783. Bibcode:1995Natur.374..783C. doi:10.1038/374783a0. Retrieved 2008-10-27. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

  Also a preprint

• Kirkwood, Daniel (1885). "Recently Discovered Asteroids". The Sidereal Messenger. 4. Northfield MN: Carleton College Observatory: 114–116. ISSN 1067-859X. Retrieved 2009-01-01.

  No new information.

• "Discovery Circumstances: Numbered Minor Planets (1)-(5000)". Harvard Univerisity Minor Planet Center.

  No new information.

• Davies, M. E. (1994). "The North Pole Direction and the Control Network of the Asteroid 243 Ida". Bulletin of the American Astronomical Society. 26: 1154. Bibcode:1994DPS....26.2502D. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
• The Asteroid Orbital Elements Database

Plan

This is a preliminary list of steps that need to be taken to finish the project

1. Write the article
   • Reorganize the old article into the new structure
   • Remove or reference any unreferenced information
   • ...
2. Illustrate the article
   • Create a gallery on this page of all the images available
   • Verify source information and complete descriptions for each image
   • Find additional free images
   • Write captions and add to the article
3. GAN (optional?)
4. Peer Review (simultaneous with GAN?)
5. FAC

DYK ideas

• ...that images of 243 Ida returned from the space probe Galileo, and processed on 17 February 1994, provided the first confirmation of a moon orbiting an asteroid?
• ...that asteroid 243 Ida is one of the most densely cratered objects in the Solar System?

External links

• Orbital simulation from JPL (Java) / Ephemeris