Wednesday, November 22, 2017

Discovering "Hot Jupiter" Exoplanets Using CUTE (Colorado Ultraviolet Transit Experiment )

Hot Jupiter illustration
Artist's depiction of vaporization of a Jupiter-sized exoplanet

In our solar system, there are no "hot Jupiters". The only Jupiter we know is a frigid (-161 C) gas giant:
Jupiter and its shrunken Great Red Spot.jpg
It is some 86,000 miles in (mean) diameter, and at a distance of 5.2 AU (778 million km) from the Sun.   Given that semi-major axis distance then by Kepler's 3rd law of planetary motion, the orbital period would be 11. 86 years.

But now consider another, distant solar system which features a "hot Jupiter" as an exoplanet.  A hot Jupiter is a giant gaseous planet that orbits close to its parent star.  Unlike Jupiter this planet  takes only a couple of days to complete a trip compared to the 88 days it takes Mercury to orbit the Sun.  How close would a planet have to be to its Sun to complete an orbit in 2 days? By  Kepler's 3rd law:

3 = P 2

Where P = 0.006 yr.  So:  a = [P 21/3   =   0.033 AU

Or, just over 3 million miles distant, which is approximately 12 times closer to its Sun than Mercury is in our own solar system.  At this close distance the parent star would dump 400 times more radiation into the nearby planet, superheating it. This would then cause the planet's atmospheric gas and particles to move ever faster until they exceed the escape velocity, shooting out of the large planet’s gravitational pull.  This would have the general appearance of a large comet - hence is  represented by the depiction shown in the graphic.

Now introduce the Colorado Ultraviolet Transit Experiment or CUTE, a shoebox-sized satellite equipped with a telescope that will launch in 2020. Its objective will be to study 12 to 20 exoplanets:  gigantic gaseous planets called “hot Jupiters, which have evaporating atmospheres trailing behind them akin to a comet.

In February, NASA allocated $3.3 million of funding for four years to the CUTE project. CUTE will leave the lab at University of Colorado-Boulder where it is being built in 2020 to hitch a ride to space along with another NASA mission. It will still be operated from the CU campus — with the help of students — as it remains in low orbit around Earth for a year, studying these “hot Jupiters.”

If all goes well, the CUTE team will ask NASA for approval to continue the research.  The candidates sought as hot Jupiters will have certain signatures for sure. In particular, the CUTE team will seek evidence for a planet which becomes "big and puffy" and  continues trucking around its star as stellar wind drags the atmosphere into a tail.

Hot Jupiters aren’t found in our solar system because no gas giants are found any nearer our Sun than Jupiter at 5.2 AU..  Our space neighborhood doesn’t even have the most common planet in the Milky Way: a "Super-Earth", or a sub-Neptune as some call it. This is a planet that’s a little bit larger by volume,  and a bit more massive than Earth.

The hot Jupiter phenomenon was first discovered with the Hubble Space Telescope.  But no such entity has ever  actually been photographed. The discovery is made by the indirect light curve method, e.g.
Image may contain: text
 Thus, any planet that passes in front of its Sun blocks most of the light. But scientists have (in this caae0 noticed times when a planet had already passed its star but the light continued to be partially blocked, as though something was trailing it. This tipped researchers off to the planets’ tails.

The CUTE team includes Kevin France - the project leader and assistant professor at the CU Laboratory for Atmospheric and Space Physics and other LASP researchers. The latter include professional research assistant Rick Kohnert, engineers and several graduate students. CU’s Astrophysical and Planetary Sciences research professor Brian Fleming is also part of the team.

Outside of CU, the CUTE team includes researchers from the University of Arizona, the Space Research Institute of the American Academy of Science in Graz, Austria, Trinity College in Dublin, Ireland, the University of Toulouse, France, and the University of Amsterdam in the Netherlands.
When asked if the CUTE acronym was intentional, one team leader (France)  let out an extended “yeah” and then started to laugh.

When casual observers ask 'what's it all for'?  France and his team deliver a solid, coherent responose - as articulated by Kevin France himself:

"All of exoplanetary science is about understanding our place in the universe. It ties into all of those big picture questions. Are we alone? Is Earth unique? Are there other solar systems like ours?"

The CUTE project will go a long way toward answering many of those questions, and the UC team should be proud of its role.

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