ESA Hubble Science Release | 2017 Sep 20
[img3="Binary Asteroid System 2006 VW139/288P - Credit: NASA, ESA, and J. AgarwalWith the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an unusual type of object in the asteroid belt between Mars and Jupiter: two asteroids orbiting each other and exhibiting comet-like features, including a bright coma and a long tail. This is the first known binary asteroid also classified as a comet. The research is presented in a paper published in the journal Nature this week.
(Max Planck Institute for Solar System Research)"]https://cdn.spacetelescope.org/archives ... c1715b.jpg[/img3][hr][/hr]
In September 2016, just before the asteroid 288P made its closest approach to the Sun, it was close enough to Earth to allow astronomers a detailed look at it using the NASA/ESA Hubble Space Telescope [1].
The images of 288P, which is located in the asteroid belt between Mars and Jupiter, revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a distance of about 100 kilometres. That discovery was in itself an important find; because they orbit each other, the masses of the objects in such systems can be measured.
But the observations also revealed ongoing activity in the binary system. “We detected strong indications of the sublimation of water ice due to the increased solar heating — similar to how the tail of a comet is created,” explains Jessica Agarwal (Max Planck Institute for Solar System Research, Germany), the team leader and main author of the research paper. This makes 288P the first known binary asteroid that is also classified as a main-belt comet.
Understanding the origin and evolution of main-belt comets — asteroids orbiting between Mars and Jupiter that show comet-like activity — is a crucial element in our understanding of the formation and evolution of the whole Solar System. Among the questions main-belt comets can help to answer is how water came to Earth [2]. Since only a few objects of this type are known, 288P presents itself as an extremely important system for future studies.
The various features of 288P — wide separation of the two components, near-equal component size, high eccentricity and comet-like activity — also make it unique among the few known wide asteroid binaries in the Solar System. The observed activity of 288P also reveals information about its past, notes Agarwal: “Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick.” ...
Comet or Asteroid? Hubble Discovers that a Unique Object is a Binary
NASA | STScI | HubbleSite | 2017 Sep 20
A binary main-belt comet - Jessica Agarwal et al
An Asteroid That Split in Two 5,000 Years Ago Is Spouting a Comet Tail
Astronomers categorize the minor bodies in the solar system according to their location and physical composition. Comets are a loose collection of ice and dust that fall in toward the Sun from beyond the orbits of the major planets, and grow long tails of dust and gas along the way. Asteroids are rocky or metallic and are relegated to a zone between Mars and Jupiter. But nature isn't that tidy. The Hubble Space Telescope photographed a pair of asteroids orbiting each other that have a tail of dust, which is definitely a comet-like feature. The odd object, called 2006 VW139/288P, is the first known binary asteroid that is also classified as a main-belt comet. Roughly 5,000 years ago, 2006 VW139/288P probably broke into two pieces due to a fast rotation.
- Nature 549(7672):357 (21 Sep 2017) DOI: 10.1038/nature23892 (preprint)
