A UCLA scientist was part of the first team of scientists to
observe distinct day and night temperatures on a planet outside our
solar system, which observations experts said could help them
better understand how distant planets function.
Distinct day and night temperatures on the planet upsilon
Andromedae b, which is located near the constellation Andromeda,
were observed by Brad Hansen, professor of astronomy and a member
of UCLA’s Institute of Geophysics and Planetary Physics, and
Joseph Harrington, professor of physics at the University of
Central Florida.
Hansen said the observation of temperature differences on
upsilon raises questions about the nature of that planet, including
how similar its composition and weather systems are to
Jupiter’s.
Observations like the ones his team made further
scientists’ understanding of how these planets, and planets
in general, work, Harrington said.
“We’ve learned more about planets that are on
different stars, and that eventually informs our study of planets
around our star and even the earth,” he said.
“It gives us access to more planets and the ability to now
start talking about how these planets’ atmospheres function,
which is essentially tied to meteorology.”
He said that though technology probably is not yet adequate to
discover Earth-like planets outside our solar system, he hopes to
use studies similar to the one recently conducted to better
understand such planets once they are discovered.
“For planet hunters, the goal is to find something that
looks like home,” Harrington said. “It’s a big
challenge to find something like that, but we’ll be there to
observe when those planets are discovered.”
Harrington said the observation of the distant star consisted of
measuring the brightness of light emitted by the planet over time
as it orbits around its star.
The planet, which rotates on its axis, orbits the star in a
sinuisodal manner, meaning that the brightness of light oscillates
up and down. The team was able to identify the day-night
temperature fluctuation by measuring the difference between the
high and low points of the brightness oscillation.
Hansen said the difference between night and day was about 2,500
degrees Fahrenheit.
Though upsilon Andromedae b is classified as a “hot
Jupiter” because it is a gas giant that orbits very close to
its scorching star, Hansen said the temperature fluctuations on
upsilon differentiate it from its namesake.
“For gas-giant planets like Jupiter, there is a lot of
wind, and this wind might take the energy from the light side and
spread (temperature) evenly around the planet,” Hansen said,
adding that scientists cannot observe differences between night and
day temperatures on Jupiter.
The fact that scientists could observe such a difference on
upsilon Andromedae b, a gas giant like Jupiter, called into
question how phenomena scientists observe on planets in the solar
system might differ in other parts of space.
The project, which was funded by NASA and used NASA’s
Spitzer Space Telescope to make its observations, is unique because
for the first time, observations were made on a planet whose
orbital plane is tilted. This means scientists can still observe
the planet-star system when the planet passes in front of its
star.
Harrington said that because the team was only interested in
comparing the light emitted over a period of time instead of
measuring the star’s absolute brightness, it was able to make
more accurate observations about temperature fluctuations on the
planet.
“As a result, our team was a factor of 50 or 100 more
accurate than the telescope was designed to be,” he said.
Hansen said roughly a 10th of one percent of the light from the
total system comes from the planet instead of its star, because the
planet re-emits light it absorbed from the star.
“When the planet is showing its day side to you,
you’re getting slightly more luminosity (from the star-planet
system),” he said. “The changes in brightness are
because you have a hot side and a cold side.”
Upsilon Andromedae b, which was discovered in 1996 by a team
based in Berkeley, is approximately 40 light years away from our
solar system and takes about four and a half days to orbit its
star.
The observations were published in the electronic version of
Science Magazine on Oct. 12 and will be in the Oct. 27 print
edition of Science.
Harrington, who has been studying planetary science for 20
years, said the analysis of the data took a few months, but the
equipment for the analysis took roughly a year to develop.