An artist's conception of a body about the size of the Moon slamming into a body the size of Mercury. As the bodies hit each other at speeds exceeding 10 km per second (about 22,400 mph), a huge flash of light is emitted, and their rocky surfaces are vaporized and melted, spraying hot matter everywhere. | |
Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Pavo |
Right ascension | 18h 45m 26.9011s |
Declination | −64° 52′ 16.533″ |
Apparent magnitude (V) | 4.8 |
Characteristics | |
Spectral type | A5 IV/V, [1] A7V (Hipparcos 2007 Catalogue) |
Astrometry | |
Distance | 95.34 ± 1.86 ly (29.23 ± 0.57 pc) |
Details | |
Mass | 2.0 [2] M☉ |
Luminosity | 9.5 [2] L☉ |
Temperature | 8,000 [1] K |
Rotational velocity (v sin i) | 175 [3] km/s |
Age | ~12, [2] ~20 [4] Myr |
Other designations | |
Database references | |
SIMBAD | data |
HD 172555 is a white-hot Type A7V star located relatively close by, 95 light years from Earth in the direction of the constellation Pavo. [5] Spectrographic evidence indicates a relatively recent collision between two planet-sized bodies that destroyed the smaller of the two, which had been at least the size of the Moon, and severely damaged the larger one, which was at least the size of Mercury. Evidence of the collision was detected by NASA's Spitzer Space Telescope. [6] [2]
HD 172555 was first recognized in the 1980s as being unusually bright in the mid-infrared by the IRAS sky survey. Follow-up ground-based observations by Schütz et al. [7] and the Spitzer Space Telescope, also in 2004, [8] confirmed the unusually strong nature of the infrared spectral emission from this system, much brighter than what would be emitted normally from the star's surface. As part of the Beta Pictoris moving group, HD 172555 is coeval with that more famous system, approximately 20 million years old, and is the same kind of white-hot star as Beta Pic, about twice as massive as the Sun and about 9.5 times as luminous. Comparison with current planetary formation theories, and with the very similar Beta Pic system, suggests that HD 172555 is in the early stages of terrestrial (rocky) planet formation.
What makes HD 172555 special is the presence of a large amount of unusual silicaceous material – amorphous silica and SiO gas – not the usual rocky materials, silicates like olivine and pyroxene, which make up much of the Earth as well. The material in the disk was analyzed in 2009 by Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory in Laurel, MD using the infrared spectrometer on board the Spitzer Space Telescope, and the results of the Deep Impact and STARDUST comet missions. [2] Analysis of the atomic and mineral composition, dust temperature, and dust mass show a massive (about a Moon's mass worth) amount of warm (about 340K) material similar to re-frozen lava (obsidian) and flash-frozen magma (tektite) as well as copious amounts of vaporized rock (silicon monoxide or SiO gas) and rubble (large dark pieces of dust) in a region at 5.8+/-0.6 AU from the HD 172555 (inside the frost line of that system). The material had to have been created in a hypervelocity impact between two large bodies; relative velocities at impacts less than 10 km/s would not transform the ubiquitous olivine and pyroxene into silica and SiO gas. Giant impacts at this speed typically destroy the incident body, and melt the entire surface of the impactee.
The implications for the detection of abundant amorphous silica and SiO gas are the following:
Follow-up VISNIR observations of the system published in 2020 have shown that the majority of observed fine dust is composed of very fine grains 1-4 micrometers diameter. [10] as expected from a recent hypervelocity impact. [11]
In 2021, a carbon monoxide ring at ~6 AU separation from the star was also found in the system by ALMA, further reinforcing a giant impact scenario for explaining the system's structure. The large amount of CO gas detected would likely have been sourced from the colliding planets' atmospheres. [12]
In 2023, the possible detection of a transit of a cometary body with a radius of approximately 2.5 km, and at a distance of 0.05 AU from the star was announced. [13]
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, because gases or other material may be falling from the inner edge of the disk onto the surface of the star. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds.
HD 107146 is a star in the constellation Coma Berenices that is located about 90 light-years (28 pc) from Earth. The apparent magnitude of 7.028 makes this star too faint to be seen with the unaided eye.
HD 210277 is a single star in the equatorial constellation of Aquarius. It has an apparent visual magnitude of 6.54, which makes it a challenge to view with the naked eye, but it is easily visible in binoculars. The star is located at a distance of 69.5 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −20.9 km/s.
BD+20°307 is a close binary star system approximately 300 light-years away in the constellation Aries. The system is surrounded by a dusty ring, and probably orbited by a 0.48M☉ white dwarf on a wide orbit.
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Iota Centauri, Latinized from ι Centauri, is a star in the southern constellation of Centaurus. Based upon parallax measurements, it lies at a distance of approximately 58.6 light-years from Earth. Iota Centauri has an apparent visual magnitude of +2.73, making it easily visible to the naked eye.
A debris disk, or debris disc, is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks are found around stars with mature planetary systems, including at least one debris disk in orbit around an evolved neutron star. Debris disks can also be produced and maintained as the remnants of collisions between planetesimals, otherwise known as asteroids and comets.
Eta Corvi is an F-type main-sequence star, the sixth-brightest star in the constellation of Corvus. Two debris disks have been detected orbiting this star, one at ~150 AU, and a warmer one within a few astronomical units (AU).
HD 98800, also catalogued as TV Crateris, is a quadruple star system in the constellation of Crater. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years away, but this value is in high error. The system is located within the TW Hydrae association (TWA), and has received the designation TWA 4.
HD 113766 is a binary star system located 424 light years from Earth in the direction of the constellation Centaurus. The star system is approximately 10 million years old and both stars are slightly more massive than the Sun. The two are separated by an angle of 1.3 arcseconds, which, at the distance of this system, corresponds to a projected separation of at least 170 AU.
HD 100546 is a star 316.4 light-years from Earth. It is orbited by an approximately 20 MJ exoplanet at 6.5 AU, although further examination of the disk profile indicates it might be a more massive object such as a brown dwarf or more than one planet. The star is surrounded by a circumstellar disk from a distance of 0.2 to 4 AU, and again from 13 AU out to a few hundred AU, with evidence for a protoplanet forming at a distance of around 47 AU.
HR 4796 is a binary star system in the southern constellation of Centaurus. Parallax measurements put it at a distance of 235 light-years from the Earth. The two components of this system have an angular separation of 7.7 arcseconds, which, at their estimated distance, is equivalent to a projected separation of about 560 Astronomical Units (AU), or 560 times the separation of the Earth from the Sun. The star and its ring resemble an eye, and it is sometimes known by the nickname "Sauron's Eye".
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An exocomet, or extrasolar comet, is a comet outside the Solar System, which includes rogue comets and comets that orbit stars other than the Sun. The first exocomets were detected in 1987 around Beta Pictoris, a very young A-type main-sequence star. There are now a total of 27 stars around which exocomets have been observed or suspected.
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