I was wondering.

I know that there was at least one study looking for the "Vulcanoids" using an F-18 flying at 49,000 feet just after sunset. I don't know what the results of that study were.

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Yes, there are several!

There are none whose orbit is entirely closer in than mecury, (in fact there is only 1 i know of whose whole orbit is closer than the earth's), but there are many currently closer than mercury. You can check out this page: http://cfa-www.harvard.edu/iau/lists/InnerPlot2.html which displays all asteroids out to mars' orbit. (From the IAU minor planet center)

There are currently 5 or so closer than merc's orbit. (But it's hard to tell becuase the diagram is 2D...)

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Here's a link about this project, although no results are mentioned.

http://news.bbc.co.uk/2/hi/science/nature/2063200.stm

__________________
"Is that a laser pointer? Well...that's fantastic! I mean...wow..that's just...GREAT!"
-Donald Rumsfeld before a Nov. 2001 speech
(His enthusiasm was muted, however, when he learned he could not guide a bomb with it.)

The F-18 project is being done by Alan Stern and Dan Durda. Search for Dan's name on the main site's search engine. He and I are old friends; we went to undergraduate school together. He is also now a columnist in Mercury magazine (I have a brief article in this month's issue as well).

So far they have not found any vulcanoids, BTW. There are pretty good upper limits on their size (or else we'd see them) and lower limits (or else radiation pressure from the Sun would blow them away). The trick is to find some on the "Goldilocks" size range.

An F18 is a rather expensive platform for astronomy. How did they get permission from the military to use one for this purpose? Are there no larger jets that can reach 49,000? It doesn't seem like that high an altitude. If only fighters can reach that altitude, you'd think an old Russian two seater like a Mig 23 could be operated for a lot less money. Excuse me if I'm sounding hypercritical. The use of an F18 is just puzzling to me. Still, it's certainly much cheaper than the shuttle.

NASA owns several old F-18s for research purposes (remember what the first "A" is in NASA). It turns out that these planes are very stable at high altitudes, like 40,000 feet, and make good platforms for observing.

I sat in one a few months ago. They are very cool, and it turns out the one I sat in is one Dan used for his research! 8)

What about Icarus(sp?)?

Icarus has a very eccentric orbit, witrh a perihelion inside Mercury's orbit; however, it also goes well outside Earth's orbit, and in fact it has a semimajor axis longer than 1 AU so is actually further away from the Sun than the Earth on average, making it officially an Apollo asteroid.

Many inner system asteroids have less eccentric orbits, and are called Aten asteroids,being on average closer to the sun than Earth;
although most of these do not get as close to the sun as Icarus.

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