| AURORA ALERTS:
Did you miss the Northern Lights of June 25th? Next time get
a wake-up call from Space
Weather PHONE. |
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AURORA WATCH: On
July 12th a solar wind stream hit Earth and sparked a geomagnetic
storm over Saskatchewan, Canada. "Alerted by a phone
call from Spaceweather, I rushed outside and got some beautiful
pictures of the auroras," says Bob Johnson of Saskatoon.
Sky watchers should be alert for a repeat tonight; the solar wind
continues to blow and NOAA forecasters estimate a 30% chance of
high-latitude geomagnetic activity: gallery.
BINARY ASTEROID: Asteroid
2008 BT18 is gliding past Earth this weekend and astronomers have
just discovered that it is a binary system. "The sizes of the
two components are 600 m for the primary and >200 m for the secondary,"
says Lance Benner of JPL. "The primary looks spheroidal, but
we don't yet know about the shape of the secondary." Benner
and others using a giant
radar in Arecibo, Puerto Rico, obtained this "delay-doppler"
image of the pair on July 7th:
"We're also getting images from NASA's Goldstone radar in
the Mojave desert of California," he adds. That radar is smaller
than Arecibo but it is still registering a strong echo that should
reveal much about the target, including the binary orbit, masses
and bulk density of the components.
About 16% of all near-Earth asteroids are binaries,
but only a handful have come this close. "2008 BT18 is giving
us a good look at a double asteroid," says Benner. Studying
the make-up and dynamics of these systems may help researchers figure
out how to deflect binaries on a collision course with Earth. 2008
BT18 poses no threat, but some undiscovered binary asteroid, one
day, might. "The Arecibo observatory,
where 53% of all near-Earth binaries have been discovered, is crucial
to these studies."
Southern hemisphere readers, you may be able to observe this double-rock
using your own backyard
telescope and CCD camera. At closest approach (1.4 million miles)
on July 14th, 2008 BT18 will flit through Canis Major heading south
and glowing like a 13th magnitude star: ephemeris,
3D
orbit.
MARS ON THE MOVE:
Put on your 3D
glasses and behold ... a "moving rock" on Mars:
Click to
view the complete scene
Graphic artist Patrick
Vantunye of Belgium created the 3D anaglyph by combining right-
and left-eye images from Phoenix's stereo camera. It shows a rock
near the Mars lander's feet seemingly pushed some distance through
the dusty soil. "It reminds me of the
moving rocks of Racetrack Playa in Death Valley," says
Vantuyne. Long held to be a mystery, those Death Valley rocks are
now
thought to travel by means of wind propulsion, skidding along
a desert floor momentarily slick after rainstorms. What moved this
Mars rock? Possibilities include Phoenix's landing thrusters, martian
wind, a nudge from Phoenix's robotic arm, and of course the unknown.
Solutions are welcomed.
SOLUTIONS: What made
the rock move? "It's a Vastitas
Borealis Gastropod,"
suggests reader Craig Weiss. That's longhand for northern martian
snail, the solution offered independently by a number of readers.
Other popular ideas, more serious ones, centered on the role of
ice. Maybe the "rock" is made of frozen water, less dense
than its rocky neighbors and more easily tumbled by Phoenix's landing
thrusters. Sublimation of ice might produce some jetting action
that would help the lump move along--like a little martian comet.
Or maybe it is just what it appears to be: a small rock, less firmly
planted in the soil than other nearby rocks, tumbled down a gentle
slope by wind or thrusters. "Upon closer inspection, I think
I have found the truth behind the moving rock," muses another
reader, Jim Mahoney. "Click
here and all will be revealed."
UPDATED: July
2008 Aurora Gallery
[Aurora Alerts] [Night-sky
Cameras]
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