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

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Mon, 12 Mar 2007 17:37:15 -0700 (MST)
Message-ID: <2796.216.53.219.122.1173746235.squirrel_at_timber.lpl.arizona.edu>

Hello List:

I have observer a few asteroids in my life and have some problems with
this article. I am away from home, so I am going mostly on memory and so
these are only estimates;

1. If you are to put a telescope at the orbit of Venus, it would have to
be in the same orbit as Venus, but not near Venus. If you are planning to
observe in the infrared, you would want a Spitzer-type telescope. The
Earth is hot and Venus would be hotter (so is the Sun)! Spitzer has a
lifetime of about 5 years thanks to shielding from the Sun and Earth. I am
not sure how much more of a problem there would be at the distance of
Venus. HST with it CCDs is much easier to cool so does not have the limits
of an infrared telescope.

2. Yes, asteroids are brighter in the infrared: but this is sunlight
absorbed and re-emitted (heat). So, yes, you could observe asteroids at
these wavelengths, but as stated about would need a cooled telescope.

3. While the idea of an asteroid "coming at us out of the sunlight"
(worked in war movies), statistically, there are fewer of these asteroid
(at least known). There are over 2000 known Apollo asteroids (cross Earth
orbit, but mean solar distance greater than Earth's) and less than 400
Aten asteroids (cross Earth's orbit, but mean distance less than Earth's).
There are known known asteroids with orbits wholly within Earth's orbit
(at least none discovered). So, there are more things coming in from
outside in than inside out. Yes, it would be "better" to look from closer
to the Sun, but would have the bigger, brighter, hotter Sun to deal with
(visible or infrared).

4. You would also be better off with more than one telescope. There is
always the chance that the asteroid with our name on it would hit us at
its first close pass (might not be able to do anything about it). But if
that is so, you would want a telescope that is looking in the direction of
the Earth at any given time.

5. Now, something that I just thought about that I cannot calculate here
in my hotel room (in Disney World). How many asteroids have perihelion
(closest distance to the Sun) that get anywhere near Venus? Most near
Earth asteroids (NEOs) can only be detected when they are close to Earth
(they are very small). These may never be detected from "far away" Venus.

That is all I can think of at the moment.

Larry

>
>
> -----Urspr?ngliche Nachricht-----
> Von: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Ron
> Baalke
> Gesendet: Freitag, 9. M?rz 2007 22:50
> An: Meteorite Mailing List
> Betreff: [meteorite-list] Could Venus Watch For Earth-Bound Asteroids?
>
>
>
> http://space.newscientist.com/article/dn11356-could-venus-watch-for-earth
> bou nd-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-
> wil l-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.
>
>
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Received on Mon 12 Mar 2007 08:37:15 PM PDT