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Pomona
College Astronomers Take Part in Rare Viewing of Pluto
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Group Project Finds Distant Planet’s Atmosphere Has
Unexpectedly Expanded
On a cloudy summer night high in the mountains above
Wrightwood, Pomona College astronomers Bryan Penprase and
Alper Ates aimed the school’s one-meter telescope at Pluto
and collected data that has helped lead to the surprising
observation that Pluto’s atmosphere has unexpectedly
expanded rather than contracted over the past 14 years. The
findings were published this month in the esteemed
scientific journal, Nature.
Penprase, associate professor of physics and astronomy and
coordinator of Pomona’s Astronomy Program, and Ates, staff
astronomer, were part of a group of astronomers stationed at
powerful telescopes around the world that same night for a
rare opportunity to view Pluto. In addition to Pomona, the
astronomers hailed from MIT, Boston University, Williams
College, Lowell Observatory and Cornell University.
“The exciting thing about the event was that Pluto was
crossing right in front of a pretty bright star. The star
could then probe through the atmosphere of Pluto and give
hints about what Pluto is made of,” said Penprase. “Alper
and I put the one-meter telescope on ‘cruise control’ so it
would track the star and automatically take pictures of
Pluto, which appeared on the screen as a small dot with the
star behind it. Our one-meter telescope was able to gather
information that, when combined with the observations of the
others and carefully studied, revealed the presence of an
atmosphere on Pluto that had expanded since a similar study
was done in 1988.”
Despite the fact that Pluto was discovered more than 80
years ago, little is known about our solar system’s most
remote planet – the only one still unvisited by spacecraft.
We know its basic size and that it has a moon named Charon –
and from the orbits of Pluto and Charon we can guess at its
mass and density. Anything else is pure conjecture.
But when a bright star passes behind Pluto, astronomers can
make some Earth-bound observations – in particular viewing
Pluto's thin atmosphere, which exerts a surface pressure
roughly a million times lower than that at the Earth's
surface. This alignment of planet and star is an uncommon
occurrence. Following the initial detection of Pluto's
atmosphere in the 1980s, there was a 14-year period during
which astronomers tried but failed to get a good view of the
planet – an unproductive time that ended with the recent
group viewing of Pluto.
Penprase said he and Ates were thrilled to participate in
the collective viewing of Pluto and they consider themselves
lucky to have such ready access to a powerful telescope.
“We were able to participate in this project easily since we
can flexibly schedule observing time on our telescope,”
Penprase said. “Many of the other observers waited for as
long as a year to get the telescope time and had to travel
thousands of miles. Alper and I were able to have dinner
with our families and then drive up to our telescope.”
Students in the Astronomy Program are making new discoveries
with the telescope, as well. For example, this summer,
juniors Millie Meier and Alex Thoreen are monitoring
protostars with the college’s new infrared camera on the
one-meter telescope. They are hoping to detect variability
in the protostars that would provide a better understanding
of how stars are formed.
To view the piece in Nature to which Penprase and Ates
contributed, go to
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v424/n6945/full/nature01762_fs.html.
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