Hubble Discovers Unusual Objects in the Asteroid Belt Spewing Water Vapor

German-led group of astronomers has observed the intriguing characteristics of a pair of unusual objects. For this observation, they used the help of Hubble Space Telescope.

The space rocks lie in the asteroid belt between Mars and Jupiter, collectively called 288P. They are two asteroids orbiting each other and don’t behave like anything previously observed in that region. They are almost the same mass and size and orbit each other at a distance of about 100 kilometers.

This is the first known binary asteroid also classified as a comet. A paper published in the journal Nature this week presented the research.

“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.

This time-lapse video made with Hubble Space Telescope photos shows two asteroids that orbit each other and have comet-like features. The asteroid pair, called 2006 VW139/288P, is unlike anything ever observed in the asteroid belt. Credit: NASA, ESA, and J. DePasquale and Z. Levay (STScI)

The unique rocks were initially identified as a single object. But follow-up observations by Agarwal and her team revealed that 288P consists of two asteroids, each about 1 kilometer (0.62 miles) wide, locked in orbit.

Another unique characteristic for two bodies is that the rock’s orbits are also highly eccentric.

Multiple factors have influenced the motion of these two objects, said Jessica Agarwal. The most surprising finding would be that the comet-like activity on the asteroids is responsible. The ejection of water vapor from the comet into space would push just a little bit on the two pieces, and perhaps, over time, send them reeling into this extreme orbit.

The Age of Asteroids

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 a refractory dust mantle, only a few meters thick, can protect them for billions of years.”

From this, the team concluded that 288P has existed as a binary system for only about 5000 years. Agarwal elaborates on the formation scenario: “The most probable formation scenario of 288P is a breakup due to fast rotation. After that, sublimation torques may have moved the two fragments further apart.”

What can we learn from this?

The rock’s strange characteristics could provide new clues about the formation of planets in the solar system, scientists said.

Understanding the origin and evolution of main-belt comets is a crucial element in our understanding of the formation and evolution of the whole Solar System. Besides that, the main-belt comets can help us know how water came to Earth.