NASA's planet-hunting
Kepler spacecraft should be able to achieve its primary mission goal regardless
of whether or not it can bounce back from a recent malfunction, researchers
say.
Kepler launched in
March 2009 on a 3.5-year prime mission to determine how common Earth-like
planets are throughout the Milky Way galaxy.
That goal is likely already
attainable, even if the spacecraft is unable to recover from the glitch that
halted its exoplanet hunt two months ago, mission team members say.
"We believe we do
have enough data to answer the question," said Kepler analysis lead Jon
Jenkins of the SETI (Search for Extraterrestrial Intelligence) Institute in
Mountain View, Calif.
"Now, we won't
have as tight error bars as we would otherwise have, and we won't have orbital
periods out well beyond Earth's in terms of Earth-size planets," Jenkins
said during a lecture last month at the SETI Institute. "But we'll still
do a credible job and a good enough job delivering the answers that we
need."
Kepler spots exoplanets
by noting the tiny brightness dips caused when they cross the face of their
parent stars. The observatory needs to see three of these "transits"
to flag an alien world, so it takes years to detect planets orbiting relatively
far from their stars.
This is precision work,
and the Kepler space telescope requires three functioning gyroscope-like
reaction wheels to stay locked onto its 150,000-plus target stars.
The observatory launched
in 2009 with four reaction wheels — three for immediate use and one spare. One
wheel, known as number two, failed in July 2012. Another (number four) stopped
working on May 11 of this year, robbing Kepler of its precision pointing
ability.
Kepler hasn't searched
for exoplanets since the latter wheel failure. Mission engineers have been
devising possible fixes for the problem, and they plan to start sending some of
these commands to the spacecraft over the next week or two.
(Launching astronauts
out to repair Kepler, as was done five separate times with NASA's Hubble Space
Telescope, is not an option. Kepler orbits the sun rather than Earth and
currently sits millions of miles from our planet.)
If at least one of the
failed wheels cannot be brought back, Kepler will almost certainly be given a
new mission, researchers say — one that emphasizes scanning instead of its
previous point-and-stare operations.
While the Kepler team
would love to continue the exoplanet hunt for years to come, researchers can likely
determine the Milky Way's frequency of Earth-like worlds with the data the
spacecraft has already collected, Jenkins said. But doing so will require a
fair bit of work.
For one thing, he said,
the team needs to continue pulling planets out of the spacecraft's huge
dataset. (To date, Kepler has detected 3,277 candidate planets, 134 of which
have been confirmed by follow-up observations. Mission scientists think at
least 90 percent of the spacecraft's finds will end up being the real deal.)
Scientists also need to
determine the completeness and reliability of Kepler's discovery system, among
other things, and understand how the mission's target stars relate to the
stellar population of the Milky Way as a whole to enable extrapolation, Jenkins
added.
The target stars
"were chosen to be really good for discovering transiting planets but
undoubtedly have selection biases in them," he said.
All of this work should
keep mission scientists busy for some time to come.
"We have about two
years of data that we have yet to fully search; we're still in the process of
searching through the third year of data," Jenkins said. "I think
that this could occupy us for another two to three years, easily."
The Kepler mission's
total pricetag is about $600 million thus far, and it costs about $20 million
per year to operate the spacecraft and analyze the data, NASA officials have
said.
Source: Yahoo news
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