Hubble May Have Discovered A Planet That Shouldn't Exist
TW Hydrae, a star located about 176 light years away, is one of the closest things in the universe we have to a time machine. That’s because it’s only about 8 million years old, and its believed to look a lot like what our own Solar System looked like in the first few million years of its existence. By studying TW Hydrae, astronomers can learn more about the history of our own Sun.
TW Hydrae and its disk. The gap may indicate the existence of a planet. (Credit: NASA/ESA)
Recently, while observing this star, the Hubble Telescope found something pretty amazing – a gap in the star’s protoplanetary disk. The disk, which was discovered a few years ago, is an accretion of large amounts of material that are expected to coalesce into a planet over the course of time. The most likely reason why such a gap would exist would be the formation of the planet. As the planet traveled around the star, its gravity would either attract or push the disk material out of its way. Such a planet would be somewhere in between 6 to 28 times more massive than Earth.
If the gap really is where a planet is located, then that planet is 7.5 billion miles from its star. That’s about twice as far as Pluto’s distance from our own Sun, making this the planet that is furthest from its parent star that we know of.
Here’s the real kicker about this planet, though: if it’s there, then current astronomical theories about how planets form are at least partially wrong. Planets are expected to form slowly over time, accumulating more and more rock and dust as it travels through the protoplanetary disk. Because planets like this are so far out from their stars, their orbits are slower and there is less material available to form a planet. Given that, it should take about 200 million years for that planet to have formed – way more years than TW Hydrae has been around.
Of course, before astronomers get out the erasers to get rid of the old theory, there’s still some work to be done. In the paper, the authors note some possible alternative explanations for the observed gap in the disk, and offer suggestions for further observations that would confirm the existence of a planet.
If it turns out there isn’t a planet, it wouldn’t be the first time TW Hydrae has gone through this. In 2007, a team of German researchers announced the discovery of a planet circling TW Hydrae. Further observations by a team of Spanish researchers in 2008, however, found that no such planet existed.