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This artist’s impression shows the binary asteroid 288P, located in the main asteroid belt between the planets Mars and Jupiter. The object is unique as it is a binary asteroid which also behaves like a comet. The comet-like properties are the result of water sublimation, caused by the heat of the Sun. The orbit of the asteroids is marked by a blue ellipse.

Earth’s Water Probably Came From Asteroids

In September 2017, an analysis of a binary asteroid helped scientists get closer to solving the mystery of Earth’s water. Binary asteroids are common in our solar system, and many asteroids even have their own moons. In 2016, the Hubble Space Telescope observed two asteroids orbiting each other as they passed by the Sun. Asteroids can range in size from a few meters, to a few hundred kilometers, such as Ceres. The binary object, now called 2006 VW139/228P, is different from typical binary asteroids; the two asteroids in 288P are only 0.6 kilometers across, and have an orbit between just 70 and 140 kilometers. So far, 288P is the only object in our solar system dubbed both a comet and an asteroid.

In a paper published in Nature, Dr. Jessica Agarwal concluded that the asteroid that it broke in half around 5,000 years ago, a result of its fast rotation. “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,” Dr. Agarwal said. Water ice on the asteroids’ surfaces gets converted into steam as 228P passes close to the Sun. The resulting water vapor forms a cometary tail, making 228P look like a comet.

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