[meteorite-list] Could Venus Watch For Earth-Bound Asteroids?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 9 Mar 2007 13:50:17 -0800 (PST)
Message-ID: <200703092150.l29LoHL22715_at_zagami.jpl.nasa.gov>

http://space.newscientist.com/article/dn11356-could-venus-watch-for-earthbound-asteroids.html

Could Venus watch for Earth-bound asteroids?
David L Chandler
New Scientist
09 March 2007

A dedicated space-based telescope is needed to achieve a congressionally
mandated goal of discovering 90% of all near-Earth asteroids down to a
size of 140 metres by the year 2020, says a report NASA sent to the US
Congress on Thursday. Asteroids of that size are large enough to destroy
a major city or region if they strike the planet - but NASA says it does
not have the money to pay for the project.

The study says Venus is the best place for the telescope. That is
because space rocks within Earth's orbit - where Venus lies - are most
likely to be lost in the Sun's glare, potentially catching astronomers
off guard. The telescope could be placed either behind or ahead of Venus
in its orbit by about 60? - the stable Lagrange points, known as L4 or
L5, where the gravity of the Sun and Venus are in balance.

"There are quite a few [objects] that are interior to Earth's orbit,"
NASA's Lindley Johnson told New Scientist. "Those are really hard to
detect [from Earth]; the opportunities to see them are very limited."

>From the orbit of Venus, however, "you're always looking away from the
Sun, always looking out", he says. "And, of course, you can observe 24
hours a day - you don't have to worry about night and day." Even from
Earth orbit, a telescope's view of any given part of the sky is blocked
about half the time by the Earth itself.

In addition, because Venus orbits the Sun in about two-thirds the time
the Earth does, a telescope in that orbit would catch up with any
near-Earth asteroids in their orbits more frequently than Earth does,
offering more opportunities for discovery. "You're able to sample that
population more rapidly in the same amount of time," Johnson says.

Missed deadline

An infrared telescope would be more effective than one that studies
visible light, because asteroids reflect sunlight more strongly at
infrared wavelengths. The background sky is also much less bright in the
infrared, providing better contrast for discovering even small, faint
asteroids.

With the Venus-orbit IR telescope, NASA could exceed its goal by three
years, finding 90% of the most dangerous space rocks by 2017. But the
space telescope is estimated to cost $1.1 billion for 15 years of
operation, and NASA says there is currently no money in its budget to
pursue any of the search proposals it studied.

That means it would take until at least 2026 to achieve its goal - and
that is assuming a large telescope in Chile called the LSST (Large
Synoptic Survey Telescope) is completed. But the LSST, which would be
funded through the National Science Foundation, itself has not had final
approval (see Unique wide-field telescope will make 'sky movies'
<http://space.newscientist.com/article/dn9200-unique-widefield-telescope-will-make-sky-movies.html>).
Without the LSST, as well, the goal would slip beyond 2030.

Former Apollo astronaut Rusty Schweickart says NASA's analysis was a
good examination of the options, and showed that "the space option ...
is most effective" in dealing with the danger of an unexpected impact.

But Schweickart says NASA failed to deliver on an additional analysis
that Congress had asked for, which included an examination of the
relative merits of different proposals for deflecting an asteroid found
to be on a collision course with Earth. "[NASA] did nothing, they
declined to respond. That's pretty disappointing," Schweickart told New
Scientist.
Received on Fri 09 Mar 2007 04:50:17 PM PST