3753 Cruithne (Asteroid) Tuesday, July 7, 2009

3753 Cruithne

Discovery
Discovered by	Duncan Waldron
Discovery date	October 10, 1986
Designations
Alternate name	1983 UH; 1986 TO
Minor planet category	Near-Earth asteroid, Venus-crosser asteroid, Mars-crosser asteroid
Orbital characteristics[1]
Epoch June 18, 2009 (JD 2455000.5)
Aphelion	226.105 Gm (1.51 AU)
Perihelion	72.415 Gm (0.484 AU)
Semi-major axis	149.260 Gm (0.998 AU)
Eccentricity	0.515
Orbital period	364.01 d (1.00 a)
Average orbital speed	27.73 km/s
Mean anomaly	170.36°
Inclination	19.81°
Longitude of ascending node	126.28°
Argument of perihelion	43.74°
Physical characteristics
Dimensions	~5 km
Mass	1.3×1014 kg
Mean density	2 ? g/cm³
Equatorial surface gravity	0.0014 m/s²
Escape velocity	0.0026 km/s
Rotation period	27.44 h[1]
Temperature	~275 K
Spectral type	?
Absolute magnitude (H)	15.1[1]

3753 Cruithne (pronounced /ˈkrɪnjə/, from Old Irish [ˈkrɪθnɛ]; Modern [ˈkrɪhnʲə] or [ˈkrɪnʲə]) is an asteroid in orbit around the Sun in 1:1 orbital resonance with that of the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit.^[2] It has been called "Earth's second moon", although it is only a quasi-satellite.^[2]

Discovery

Cruithne was discovered on October 10, 1986, by Duncan Waldron on a photographic plate taken with the UK Schmidt Telescope at Siding Spring Observatory, Coonabarabran, Australia. The 1983 apparition (1983 UH) is credited to Giovanni de Sanctis and Richard M. West of the European Southern Observatory in Chile. It was not until 1997 that its unusual orbit was determined by Paul Wiegert and Kimmo Innanen, working at York University in Toronto, and Seppo Mikkola, working at the University of Turku in Finland.

The asteroid is named after the Cruithne people (also known as the Priteni or the Picts) who inhabited Scotland and parts of Ireland and the Isle of Man between 800 BCE and 1000 CE^{[citation needed]}; the name may specifically refer to their legendary first leader, also called Cruithne.

Dimensions and orbit

Cruithne and Earth seem to follow each other in their orbits.

Cruithne appears to make a bean-shaped orbit from the perspective of Earth.

Cruithne's distance to Earth and the Sun plotted over 500 years (top) and 10 years (bottom).

Cruithne is approximately 5 km in diameter, and its closest approach to Earth is approximately 30 times the separation between Earth and the Moon (12 Gm or million kilometres). From 1994 through 2015, Cruithne will make its annual closest approach to Earth every November.^[3] Although Cruithne's orbit is not thought to be stable over the long term, calculations by Wiegert and Innanen showed that it has likely been synchronized with Earth's orbit for a long time. There is no danger of a collision with Earth for millions of years, if ever. Its orbital path and Earth's do not cross, and its orbital plane is currently tilted to that of the Earth by 19.8°. Cruithne, having a maximum opposition magnitude of +15.8, is fainter than Pluto and would require at least a 12.5-inch (320 mm) reflecting telescope to be seen.^[4][5]

Cruithne is in a normal elliptic orbit around the Sun. Its period of revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth. Because of this, Cruithne and Earth appear to "follow" each other in their paths around the Sun. This is why Cruithne is sometimes called "Earth's second moon".^[2] However, it does not orbit the Earth and is not a moon.^[6] In 2058, Cruithne will come within 0.09 AU (13.6 million kilometres) of Mars.^[3] Cruithne's distance from the Sun and orbital speed vary a lot more than the Earth's, so from the Earth's point of view Cruithne actually follows a kidney bean-shaped horseshoe orbit ahead of the Earth, taking slightly less than one year to complete a circuit of the "bean". Because it takes slightly less than a year, the Earth "falls behind" the bean a little more each year, and so from our point of view, the circuit is not quite closed, but rather like a spiral loop that moves slowly away from the Earth.

After many years, the Earth will have fallen so far behind that Cruithne will then actually be "catching up" on the Earth from "behind". When it eventually does catch up, Cruithne will make a series of annual close approaches to the Earth and gravitationally exchange orbital energy with Earth; this will alter Cruithne's orbit by a little over half a million kilometres (whilst Earth's orbit is altered by about 1.3 centimetres) so that its period of revolution around the Sun will then become slightly more than a year. The kidney bean will then start to migrate away from the Earth again in the opposite direction — instead of the Earth "falling behind" the bean, the Earth is "pulling away from" the bean. The next such series of close approaches will be centred on the year 2292 — in July of that year, Cruithne will approach Earth to about 12.5 million km.

After 380 to 390 years or so, the kidney-bean-shaped orbit approaches Earth again from the other side, and the Earth, once more, alters the orbit of Cruithne so that its period of revolution around the Sun is again slightly less than a year (this last happened with a series of close approaches centred on 1902, and will next happen with a series centered on 2676). The pattern then repeats itself.

Similar minor planets

Figure 1. Plan showing possible orbits along gravitational contours (Not to scale)

More near-Earth objects (NEOs) have since been discovered. These include 54509 YORP, (85770) 1998 UP₁, 2002 AA₂₉, and 2009BD which exist in resonant orbits similar to Cruithne's.

Other examples of natural bodies known to be in horseshoe orbits include Janus and Epimetheus, natural satellites of Saturn. The orbits these two moons follow around Saturn are much simpler than the one Cruithne follows, but operate along the same general principles.

Mars has four known co-orbital asteroids (5261 Eureka, 1999 UJ₇, 1998 VF₃₁, and 2007 NS₂, all at the Lagrangian points), and Jupiter has many (more than 1000 known objects, the Trojan asteroids); there are also other small co-orbital moons in the Saturnian system: Telesto and Calypso with Tethys, and Helene and Polydeuces with Dione. However, none of these follow horseshoe orbits.

See also

• 2006 RH₁₂₀
• Asteroids in fiction: Other asteroids, Asteroids in fiction: Colonization, and Asteroids in fiction: Mining
• Co-orbital moon
• Earth's second moon
• Natural satellite
• Quasi-satellite
• Steven Baxter's "Manifold: Time", a novel in which Cruithne plays a major role; nominated for the Arthur C. Clarke science fiction award in 2000

624 Hektor (Asteroid)

624 Hektor

Discovery
Discovered by	August Kopff
Discovery date	February 10, 1907
Designations
Alternate name	1907 XM; 1948 VD
Minor planet category	Trojan asteroid
Orbital characteristics[1]
Epoch October 22, 2004 (JD 2453300.5)
Aphelion	800.220 Gm (5.349 AU)
Perihelion	762.145 Gm (5.095 AU)
Semi-major axis	781.183 Gm (5.222 AU)
Eccentricity	0.024
Orbital period	4358.521 d (11.93 a)
Average orbital speed	13.03 km/s
Mean anomaly	94.752°
Inclination	18.198°
Longitude of ascending node	342.791°
Argument of perihelion	183.579°
Physical characteristics
Dimensions	370 km × 195 km × 195 km[2]
Mass	~1.4×1019 kg
Mean density	2 ? g/cm³
Equatorial surface gravity	~0.067 m/s²
Escape velocity	~0.13 km/s
Rotation period	0.2884 d (6.92 h)[3]
Albedo	0.025 (geometric)[1]
Temperature	~122 K
Spectral type	D
Apparent magnitude	13.79 to 15.26
Absolute magnitude (H)	7.49[1]
Angular diameter	0.078" to 0.048"

624 Hektor (pronounced /ˈhektɔr/ HEK-tor) is the largest of the Jovian Trojan asteroids. It was discovered in 1907 by August Kopff.

Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, L₄, called the 'Greek' node after one of the two sides in the legendary Trojan War. Ironically, Hektor is named after the Trojan hero Hektor, and is thus one of two Trojan asteroids that is "misplaced" in the wrong camp (the other being 617 Patroclus in the Trojan node).

Hektor is one of the most elongated bodies of its size in the solar system, being 370 × 200 km. It is thought that Hektor might be a contact binary (two asteroids joined by gravitational attraction) like 216 Kleopatra. Hubble Space Telescope observations of Hektor in 1993 did not show an obvious bilobated shape because of a limited angular resolution. On July 17 2006, the Keck-10m II telescope and its Laser guide star Adaptive Optics (AO) system indicated a bilobated shape for Hektor. Additionally, since this AO system provides an excellent and stable correction (angular resolution of 0.060 arcsec in K band), a 15-km moonlet at 1000 km of Hektor's primary was detected. The satellite's provisional designation is S/2006 (624) 1^[4]. Hektor is, so far, the only known binary trojan asteroid in the L₄ point and the first Trojan with a satellite companion. 617 Patroclus, another large Trojan asteroid located in the L₅, is composed of two same-sized components.

324 Bamberga (Asteroid)

324 Bamberga

Discovery A
Discoverer	Johann Palisa
Discovery date	February 25, 1892
Alternate designations B	none
Category	Main belt
Orbital elements C
Epoch 30 January 2005 (JD 2453400.5)
Eccentricity (e)	0.338
Semi-major axis (a)	401.409 Gm (2.683 AU)
Perihelion (q)	265.576 Gm (1.775 AU)
Aphelion (Q)	537.241 Gm (3.591 AU)
Orbital period (P)	1605.397 d (4.4 a)
Mean orbital speed	18.18 km/s
Inclination (i)	11.107°
Longitude of the ascending node (Ω)	328.058°
Argument of perihelion (ω)	44.062°
Mean anomaly (M)	4.564°
Physical characteristics D
Diameter	229 km[1][2]
Mass	1.1×1019 kg[3]
Density	1.8 g/cm³
Surface gravity	0.014 m/s²
Escape velocity	0.23 km/s
Rotation period	1.226 d[4] (29.43 h)[1]
Spectral class	C-type asteroid[5]
Absolute magnitude	6.82[1][2]
Albedo (geometric)	0.0628[1][2]
Mean surface temperature	~172 K
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324 Bamberga (pronounced /bæmˈbɜrɡə/ bam-BER-gə) is one of the largest asteroid in the Main asteroid belt. It was discovered by Johann Palisa on February 25, 1892 in Vienna, making it one of the last large (diameter over 200 km) asteroids discovered. Apart from the near-earth asteroid Eros, it was the last asteroid which is ever easily visible with binoculars to be discovered.

Although its very high orbital eccentricity means its opposition magnitude varies greatly, at a rare opposition near perihelion Bamberga can reach a magnitude of +8.0^[6], which is as bright as Saturn's moon Titan. Such near-perihelion oppositions occur on a regular cycle every twenty-two years, with the last occurring in 1991 and the next in 2013. Its brightness at these rare near-perihelion oppositions makes Bamberga the brightest C-type asteroid, roughly one magnitude brighter than 10 Hygiea's maximum brightness of around +9.1. At such an opposition Bamberga can in fact be closer to Earth than any main belt asteroid with magnitude above +9.5, getting as close as 0.78 AU. For comparison, 7 Iris never comes closer than 0.85 AU and 4 Vesta never closer than 1.13 AU when it becomes visible to the naked eye in a light pollution-free sky.

Overall Bamberga is the tenth brightest main belt asteroid after, in order, Vesta, Pallas, Ceres, Iris, Hebe, Juno, Melpomene, Eunomia and Flora. Its high eccentricity (for comparison 36% higher than that of Pluto), though, means that at most oppositions other asteroids reach higher magnitudes.

It has an unusually long rotation period among the large asteroids. Its spectral class is intermediate between the C-type and P-type asteroids.^[5]

An occultation of Bamberga was observed on 8 December 1987, and gave a diameter of about 228 km, in agreement with IRAS results.

15 Eunomia (Asteroid)

15 Eunomia

Discovery
Discovered by	Annibale de Gasparis
Discovery date	July 29, 1851
Designations
Alternate name	none
Minor planet category	Main belt, (Eunomia family)
Orbital characteristics[1]
Epoch June 14, 2006 (JD 2453900.5)
Aphelion	469.429 Gm (3.138 AU)
Perihelion	321.429 Gm (2.149 AU)
Semi-major axis	395.429 Gm (2.643 AU)
Eccentricity	0.187
Orbital period	1569.687 d (4.30 a)
Average orbital speed	18.16 km/s
Mean anomaly	286.102°
Inclination	11.738°
Longitude of ascending node	293.273°
Argument of perihelion	97.909°
Physical characteristics
Dimensions	357×255×212 km[2] 268 km (mean) 330×245×205[3][4][5] 255.33 km IRAS[1]
Mass	3.12 × 1019 kg[2]
Mean density	3.09 ± 0.52 g/cm³[2] 3.8±0.7 g/cm³[6] (based on IRAS diameter of 255km)
Equatorial surface gravity	0.08 m/s²
Escape velocity	0.16 km/s
Rotation period	0.2535 d (6.083 h)[1][7]
Albedo	0.209 (geometric)[1]
Temperature	~166 K max: 260 K (-13 °C)
Spectral type	S-type asteroid[1]
Apparent magnitude	7.9[8] to 11.24
Absolute magnitude (H)	5.28[1]
Angular diameter	0.29" to 0.085"

15 Eunomia (pronounced /jʊˈnoʊmiə/ ew-NOH-mee-ə, Greek: Ευνομία) is a very large asteroid in the inner main asteroid belt. It is the largest of the stony (S-type) asteroids, and somewhere between the 8th to 12th largest Main Belt asteroid overall (uncertainty in diameters causes uncertainty in its ranking). It is the largest member of the Eunomia family of asteroids, and is estimated to contain 1% of the total mass of the asteroid belt.^[6][9]

Eunomia was discovered by Annibale de Gasparis on July 29, 1851 and named after Eunomia, one of the Horae (Hours), a personification of order and law in Greek mythology.

Characteristics

As the largest S-type asteroid (with 3 Juno being a very close second), Eunomia has attracted a moderate amount of scientific attention. It contains slightly over one percent of the mass of the entire main belt.

Eunomia appears to be an elongated but fairly regularly shaped body, with what appear to be four sides of differing curvature and noticeably different average compositions.^[4] Its elongation led to the suggestion that Eunomia may be a binary object. However, this has been refuted.^[5] It is a retrograde rotator with its pole pointing towards ecliptic coordinates (β, λ) = (-65°, 2°) with a 10° uncertainty.^[4][5] This gives an axial tilt of about 165°.

Like other true members of the family, its surface is composed of silicates and some nickel-iron, and is quite bright. Calcium-rich pyroxenes and olivine, along with nickel-iron metal have been detected on Eunomia's surface. Spectroscopic studies suggest that Eunomia has regions with differing composition. A larger region dominated by olivine, which is pyroxene poor and metal rich, and another somewhat smaller region on one hemisphere (the less pointed end) that is noticeably richer in pyroxene,^[4] and has a generally basaltic composition.^[10]

This composition indicates that the parent body was likely subject to magmatic processes, and became at least partially differentiated under the influence of internal heating in the early period of the Solar System. The range of compositions of the remaining Eunomia family members, formed by a collision of the common parent body, is large enough to encompass all the surface variations on Eunomia itself. Interestingly, the majority of smaller family members are more pyroxene rich than Eunomia's surface, and contain very few metallic (M-type) bodies.

Altogether these lines of evidence suggest that Eunomia is the central remnant of the parent body of the Eunomia family that was stripped of most of its crustal material by the family-forming impact, but perhaps not disrupted. However, there is uncertainty over Eunomia's internal structure and relationship to the family parent body. Computer simulations of the collision^[11] are more consistent with Eunomia being a re-accumulation of most of the fragments of a completely shattered parent body. Coversely again, Eunomia's quite high density would indicate that it is not a rubble pile after all. Whetever the case in this respect, it appears that any metallic core region, if present, has not been exposed.

An older explanation of the compositional differences, that Eunomia is a mantle fragment of a far larger parent body (with a bit of crust on one end, and a bit of core on the other) appears to be ruled out by studies of the mass distribution of the entire Eunomia family of asteroids. These indicate that the largest remaining fragment (that is, Eunomia) should have about 70% of the mass of the parent body,^[12] which is consistent with Eunomia being a central remnant, with the crust and a part of the mantle stripped off.

These indications are also in accord with fresh mass determinations which indicate that Eunomia has a typical density for mostly intact stony asteroids, and not the anomalously low "rubble pile" density of ~1 g/cm³ that had been obtained earlier.

Eunomia has been observed occulting stars three times. It has a mean opposition magnitude of +8.5,^[13] about equal to the mean brightness of Titan and can reach +7.9 at a near perihelion opposition.

2101 Adonis(Asteroid)

2101 Adonis

Discovery
Discovered by	Eugene Delporte
Discovery date	February 12, 1936
Designations
Alternate name	1936 CA
Minor planet category	Apollo, Mars crosser
Orbital characteristics
Epoch October 22, 2004 (JD 2453300.5)
Aphelion	494.673 Gm (3.307 AU)
Perihelion	65.906 Gm (0.441 AU)
Semi-major axis	280.289 Gm (1.874 AU)
Eccentricity	0.765
Orbital period	936.742 d (2.56 a)
Average orbital speed	18.10 km/s
Mean anomaly	307.406°
Inclination	1.349°
Longitude of ascending node	350.580°
Argument of perihelion	42.438°
Physical characteristics
Dimensions	0.5—1.2 km 1
Mass	0.13—1.8×1012 kg
Mean density	2.0? g/cm³
Equatorial surface gravity	0.0001—0.0003 m/s²
Escape velocity	0.0003—0.0006 km/s
Rotation period	? d
Albedo	0.20—0.04 1
Temperature	197—207 K
Spectral type	?
Absolute magnitude (H)	18.7

2101 Adonis was one of the first near-Earth asteroids to be discovered. It was discovered by Eugene Delporte in 1936 and named after Adonis, the beautiful youth with whom the goddess Venus fell in love. Adonis is believed to measure approximately 1 km in diameter.

In the close approach that led to its initial discovery, not enough observations could be made to calculate an orbit, and Adonis was a lost asteroid until 1977 when it was rediscovered by Charles T. Kowal.

Adonis was the second Apollo asteroid to be discovered (after 1862 Apollo itself). It may be an extinct comet, and may be the source of some meteor showers.^[1]

Adonis makes close approaches to Venus, Earth, and Mars.^[2] It comes within 30 Gm of the Earth six times in the 21st century, the nearest being 5.3 Gm in 2036.^[3]

Adonis in fiction

See Asteroids in fiction.

In the 1954 Tintin comic book Explorers on the Moon, a drunken Captain Haddock almost becomes a satellite of the asteroid, which is improbably depicted passing between the Earth and the Moon.

1566 Icarus Asteroid)

1566 Icarus

Discovery
Discovered by	Walter Baade
Discovery date	June 27, 1949
Designations
Alternate name	1949 MA
Minor planet category	Apollo asteroid, Mercury-crosser asteroid, Venus-crosser asteroid, Mars-crosser asteroid
Orbital characteristics
Epoch July 14, 2004 (JD 2453200.5)
Aphelion	294.590 Gm (1.969 AU)
Perihelion	27.923 Gm (0.187 AU)
Semi-major axis	161.257 Gm (1.078 AU)
Eccentricity	0.827
Orbital period	408.778 d (1.12 a)
Average orbital speed	22.88 km/s
Mean anomaly	124.422°
Inclination	22.854°
Longitude of ascending node	88.090°
Argument of perihelion	31.290°
Physical characteristics
Dimensions	1.4 km
Mass	2.9×1012 kg
Mean density	2 ? g/cm³
Equatorial surface gravity	0.000 39 m/s²
Escape velocity	0.000 74 km/s
Rotation period	0.094 71 d
Albedo	0.4[1]
Temperature	~242 K
Spectral type	U
Absolute magnitude (H)	16.9

1566 Icarus (pronounced /ˈɪkərəs/ ik'-ə-rəs) is an Apollo asteroid (a sub-class of near-Earth asteroid) whose unusual characteristic is that at perihelion it is closer to the Sun than Mercury; it is said to be a Mercury-crosser asteroid. It is also a Venus and Mars-crosser. It is named after Icarus of Greek mythology, who flew too close to the Sun. It was discovered in 1949 by Walter Baade.

Icarus makes a close approach to Earth at gaps of 9, 19, or 38 years. Rarely, it comes as close as 6.4 Gm (16 lunar distances and 4 million miles), as it did on June 14, 1968. The last close approach was in 1996, at 15.1 Gm, almost 40 times as far as the Moon. ^[2] The next close approach will be June 16, 2015 at 8.1 Gm (5 million miles).

In 1967, Professor Paul Sandorff from the Massachusetts Institute of Technology gave his students the task to devise a plan to destroy Icarus in the case that it was on a collision course with Earth. This plan is known as Project Icarus^[3] (which was the basis for the 1979 science fiction film Meteor, starring Sean Connery).

References

1. ^ Radiometry of near-earth asteroids
2. ^ Page Modified
3. ^ Project Icarus, MIT Report No. 13, MIT Press 1968, edited by Louis A. Kleiman. "Interdepartmental Student Project in Systems Engineering at the Massachusetts Institute of Technology, Spring Term, 1967".