Astronomy Picture of the Day 5-04-02

NASA ^ | 5-04-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 May 4

The Moons of Earth
Credit: STS-91 Crew, NASA

Explanation: While orbiting the planet during their June 1998 mission, the crew of the Space Shuttle Discovery photographed this view of two moons of Earth. Thick storm clouds are visible in the lovely blue planet's nurturing atmosphere and, what was then Earth's largest artificial moon, the spindly Russian Mir Space Station can be seen above the planet's limb. The bright spot to the right of Mir is Earth's very large natural satellite, The Moon. The Mir orbited planet Earth once every 90 minutes about 200 miles above the planet's surface or about 4,000 miles from Earth's center. The Moon orbits once every 28 days at a distance of about 250,000 miles from the center of the Earth.

[petuniasevan]

This photo was taken in 1998. MIR re-entered Earth's atmosphere in a "controlled deorbit" March 23, 2001. The pieces landed in the South Pacific.

Get on the APOD PING list!

[petuniasevan]

APOD PING!

[dansangel]

Thanks for the ping....APOD bump!

[RightWhale]

Seriously though, earth does have two moons. The second one is in a radical polar orbit; some say it is just an asteroid, but its orbit, while not elliptical, is earth-centered.

[petuniasevan]

Yes, that's true - in a way. However, this "second moon", actually asteroid 3753 Cruithne, is not in a permanently stable orbit. For now, though, its quite elliptical orbit (quite inclined with respect to the orbital plane of the Solar System) has a resonance of 1:1 with Earth, and its oscillation period is somewhere around 760-770 years. However, the orbital stability projections begin to break down in 5000 years and completely destabilize by 10000 years.

A good site for java illustrations of this asteroid and its orbit, compared to Earth and other planets, is this LINK.

In addition, there are now two more near-Earth asteroids known to be currently in resonant states similar to those of Cruithne. These are 1998 UP1 and 2000 PH5.

[RightWhale]

Cruithne

That is the one. It is a candidate for early asteroid mining, although it is uncertain if it could be a carbonaceous chondrite. If it is, it's better than a gold mine. If not, it's just an iron mine or a science outpost.

[petuniasevan]

Looks like our technical jargon scared away the regular posters...

[RightWhale]

Let's add a little more technical info, maybe a lurker will be interested. Cruithne's orbit, as seen from the earth, is horseshoe-shaped. When it is near the earth, it is at one end or the other of the horseshoe and above one or the other pole. It would be relatively easy to hop over there, and we should do that as soon as possible. If it is carbonaceous chondrite, that means it has everything a base would need, including water. This needs to be checked out.

[herewego]

Please ping me so the stars I may see.

[petuniasevan]

Next pass will be under the South Pole at about .3 AU, or around 28 million miles. That's a bit of a trip.
It never gets closer than .1 AU, about 40 times the Earth-Moon distance. And that won't happen in the near future.

Still, we have to move into the "deep end" sometime...space exploration has really hit the skids since I was a goggle-eyed kid watching Armstrong and Aldrin bounce around on the moon.