Monday, April 20, 2020

Inbox Astronomy: Exoplanet Apparently Disappears in Latest Hubble Observations


Exoplanet Apparently Disappears in Latest Hubble Observations

Release date: Apr 20, 2020 3:00 PM (EDT)

What do astronomers do when a planet they are studying suddenly seems to disappear from sight? In the legendary Star Wars galaxy (you know, "a long time ago and far, far away") the planet might have been the victim of the evil empire's planet-zapping Death Star. But this is pretty improbable in our own cosmic back yard. The missing-in-action planet was last seen orbiting the star Fomalhaut, just 25 light-years away. (In fact, Fomalhaut is so close to us that it's one of the brightest stars in the sky, in the constellation of Pisces Austrinus, the Southern Fish.)

A team of researchers from the University of Arizona believe a full-grown planet never existed in the first place. Instead, they concluded that the Hubble Space Telescope was looking at an expanding cloud of very fine dust particles from two icy bodies that smashed into each other. Hubble came along too late to witness the suspected collision, but may have captured its aftermath. This happened in 2008, when astronomers eagerly announced that Hubble took its first image of a planet orbiting another star. The diminutive-looking object appeared as a dot next to a vast ring of icy debris encircling Fomalhaut. In following years, they tracked the planet along its trajectory. But over time the dot, based on their analysis of Hubble data, got fainter until it simply dropped out of sight, say the researchers, as they pored through the Hubble archival data.

Asteroid families in our own solar system are considered fossil relics of such collisions which happened here billions of years ago, in the solar system's rambunctious youth. But no such cataclysm has ever been seen happening around another star. Why? In the case of Fomalhaut, such smashups are estimated to happen once every 200,000 years. Therefore, Hubble astronomers may have been lucky enough to be looking at the right place at the right time.

Follow-up observations will likely be needed to test this startling conclusion.

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