Click for larger version. Credit: NASA, ESA, J. Debes (STScI), H. Jang-Condell (University of Wyoming), A. Weinberger (Carnegie Institution of Washington), A. Roberge (Goddard Space Flight Center), G. Schneider (University of Arizona/Steward Observatory), A. Feild (STScI/AURA)
So far, thousands of exoplanets and exoplanet candidates have been found orbiting other stars. As well, astronomers have seen some exoplanets still in the process of formation, providing clues as to how our own solar system came to be. One of these recent “planet-under-construction” findings however is challenging current theories on planetary formation – it’s a planet which “shouldn’t be there” according to conventional wisdom.
The probable planet in question orbits the red dwarf star TW Hydrae, about 176 light-years from Earth. The young star is still surrounded by a protoplanetary disk of gas and dust from which planets can form.
What Hubble found is a gap in that disk, about 3 billion kilometres (1.9 billion miles) wide. The planet is thought to be forming inside that gap, as is typical, as the forming planet “sweeps up” nearby dust, rocks and gas. What’s unusual is how far out the planet is from its star, approximately 12 billion kilometres (7.5 billion miles), twice the distance that Pluto orbits our sun. That’s a long ways out.
The problem is that planets take a long time to form, gradually coalescing from the dust, rocks and gas in the disk. It is estimated that a planet at that distance from its star would take about 10 million years to form. But the star, TW Hydrae, is thought to be only about 8 million years old. Scientists will now have to try to figure out the apparent discrepancy.
“It’s so intriguing to see a system like this,” said John Debes of the Space Telescope Science Institute in Baltimore. “This is the lowest-mass star for which we’ve observed a gap so far out.”
He adds, “If we can actually confirm that there’s a planet there, we can connect its characteristics to measurements of the gap properties. That might add to planet formation theories as to how you can actually form a planet very far out.”
It’s possible that a portion of the protoplanetary disk collapsed on itself, which could allow a planet to form in only a few thousand years.
Another good example of how much we learn, there is always more that we don’t yet know or understand about the incredible universe we live in.
This article was first published on Examiner.com.