[meteorite-list] Deep Impact Extended Mission Could Probe Deeper Into Solar System Origin

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 13 Apr 2007 14:43:13 -0700 (PDT)
Message-ID: <200704132143.l3DLhDf13939_at_zagami.jpl.nasa.gov>

http://www.nasa.gov/centers/goddard/news/topstory/2007/epoxi.html

Deep Impact Extended Mission Could Probe Deeper Into Solar System Origin
Bill Steigerwald
NASA Goddard Space Flight Center
April 5, 2007

In July, 2005, the Deep Impact spacecraft released a probe that blasted
a crater in comet Tempel 1, spilling its elements into space so
scientists could discover its composition. The assault was justified
because comets are thought to be leftovers from the formation of our
solar system, so learning more about them helps to understand how our
solar system came to be.

Since those fireworks, the spacecraft has cruised silently through
space, healthy and able to take on another mission, if needed. The Deep
Impact team realized that with the spacecraft already built and
launched, extra discoveries could be made at very little cost, a bonus
for an already successful mission.

The team put together a proposal to use the spacecraft's telescope to
observe the atmospheres of alien worlds, and to visit another comet. The
proposed extended mission is called EPOXI (Extrasolar Planet Observation
and Deep Impact Extended Investigation), and it has received $500,000
from NASA for an initial study to determine the requirements and costs
in greater detail.

If approved, as Deep Impact passes by Earth on December 31, 2007, it
will use our planet's gravity to direct itself to comet Boethin. While
it cruises toward the comet, the first part of the extended mission --
the investigation of alien worlds --would begin in January, 2008. More
than 200 alien (extrasolar) planets have been discovered to date. Most
of these are detected indirectly, by the gravitational pull they exert
on their parent star. Directly observing extrasolar planets is very
difficult, because the star is so brilliant compared to the planet.
Planets simply get lost in the glare, like fireflies near a headlight.

However, sometimes by chance the orbit of an extrasolar planet is
aligned so that it eclipses its star as seen from Earth. In these rare
cases, light from the extrasolar world can be seen directly. "When the
planet appears next to its star, your telescope captures their combined
light. When the planet passes behind its star, your telescope only sees
light from the star. By subtracting light from just the star from the
combined light, you are left with light from the planet. We can analyze
this light to discover what the atmospheres of these planets are like,"
said Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md.,
Deputy Principal Investigator for EPOXI.

Deep Impact will observe three nearby stars with "transiting extrasolar
planets," so named because the planet transits, or passes in front of,
its star. The planets were discovered earlier and are giant planets with
massive atmospheres, like Jupiter in our solar system. They orbit their
stars much closer than Earth does the sun, so they are hot and belong to
the class of extrasolar planets nicknamed "Hot Jupiters".

These giant planets may not be alone. If there are other worlds around
these stars, they might also transit the star and be discovered by the
spacecraft. Even if they don't transit, Deep Impact could find them
indirectly. Their gravity will pull on the transit planets, altering
their orbits and the timing of their transits. "Since Deep Impact will
be able to stare at these stars for long periods, we can observe
multiple transits and compare the timing to see if there are any hidden
worlds," said Deming.

Around May of 2008, the extended mission will transition to the second
phase as the spacecraft approaches comet Boethin. In mid-December 2008,
Deep Impact will come within 700 kilometers (435 miles) of Boethin.
Passing by at more than 10 kilometers per second (6.2 miles per second),
Deep Impact will only have about a half-dozen hours to make detailed
observations.

"The comet hit by Deep Impact's probe, Tempel 1, was unusual compared to
other comets we have seen up close," said Michael A'Hearn of the
University of Maryland, College Park, Principal Investigator for EPOXI.
For example, it appears that several pieces may have come together to
build up the comet's nucleus, the lump of ice and dust that comprises
the solid part of a comet. Second, comets vent gases as they come closer
to the sun and warm up. Tempel 1 did this as well, but in an unusual
way. Water vapor vents appeared all over the nucleus, as expected, but
carbon dioxide only vented from certain parts. Also, since comets are a
mixture of dust and ice, scientists expected dust to be dragged out from
any gas vent, but dust only came from the carbon dioxide vents. Third,
there are some very smooth areas on the nucleus, as if something had
flowed there. However, the comet's gravity is extremely weak, so
scientists don't understand how any material could be pulled down to
flow across the surface. Finally, there are circular areas with raised
rims that resemble impact craters. However, craters haven't been seen on
any other visited comets so far. Scientists are surprised to see them on
Tempel 1 because it's hard to understand how craters would last, since
the surface gets vaporized every time the comet's orbit takes it close
to the sun.

"We want a close look at Boethin to see if the surprises of Tempel 1 are
more common than we thought, or if Tempel 1 really is unusual," said
A'Hearn.

Deep Impact does not have another probe, so Boethin will not get hit,
but the close-up view will allow the spacecraft's infrared spectrometer
to make a map of the comet's surface composition, while the telescope
observes surface features.

"It's exciting that we were able to combine two totally independent
science investigations into a single project. However, both relate to
understanding how solar systems form and evolve," said A'Hearn.

According to the team, comets and their asteroid kin are the leftover
building blocks of planets, and might have contributed water and organic
material to the ancient Earth, aiding the start of life. By observing
extrasolar planets, scientists can compare them to our own and discover
what we have in common, what we don't, and perhaps why.

"The EPOXI mission is short, sweet, focused, and gives a rich science
return," said Deming.

Elements of the EPOXI mission were among approximately two dozen
proposals submitted in response to NASA's Discovery Program 2006
Announcement of Opportunity last April. NASA selected three proposed new
Discovery-class missions, and three "mission of opportunity" proposals
that would make use of existing NASA spacecraft, for concept development
funding. Two of the three existing spacecraft proposals used the Deep
Impact spacecraft, and were later combined into the EPOXI proposal. NASA
may select one or more investigations to continue into a development
effort after detailed review of the concept studies. Decisions about
which mission concepts will proceed to development are expected in late
2007. If selected, the EPOXI project will be managed by NASA's Jet
Propulsion Laboratory in Pasadena, Calif.
Received on Fri 13 Apr 2007 05:43:13 PM PDT