[FMO] Asteroid to hit Mars (Fwd: NEO News (12/21/07) "Tunguska" on Mars?)

From: Marco Langbroek <marco.langbroek@xxxxxxxxxx>
To: FMO lijst <fmo@xxxxxxxxxxxxx>
Date: Sat, 22 Dec 2007 12:30:52 +0100


-------- Originele bericht --------
Onderwerp: NEO News (12/21/07) "Tunguska" on Mars?
Datum: Fri, 21 Dec 2007 10:33:34 -0800
Van: David Morrison <david.morrison@xxxxxxxx>
Aan: David Morrison <david.morrison@xxxxxxxx>

NEO News (12/21/07) "Tunguska" on Mars?

Remarkably, the Spaceguard Survey has discovered
a small NEA that might hit Mars, not Earth, Orbit
calculations from JPL indicate that Asteroid 2007
WD5 is on a trajectory that will bring it close
to Mars on January 30, with a chance of hitting
(based on the current uncertainty in the orbit)
of better than 1%. Only once (3 years ago) has
the orbital analysis of a NEA indicated a higher
probability of impact, and the target then was
Earth. For about two days around Christmas, 2004,
the calculated impact probability for NEA Apophis
was better than 1%, reaching a maximum of
slightly greater than 1 in 50. Of course,
additional orbital data then showed that while
Apophis would come close in April 2029, it would
not hit. The same thing will probably happen with
this orbital analysis of 2007 WD5. But those of
us in the business of surveying for possible
impacts must always consider the possibility of a
hit, even if the odds are against it. Should 2007
WD5 actually hit Mars, it would have an impact
energy similar to that of the 1908 Tunguska
impact on Earth, making a roughly 1-km-diameter
crater. This crater, with its freshly exposed
ejecta, would be extremely interesting to study
from several spacecraft now in orbit around Mars.
We can hope that this might happen, providing us
a new window into the martian subsurface -- but
the most likely ending for this story will be a
miss, with 2007 WD5 quickly fading from memory.

Below are two press stories about 2007 WD5, and
another reporting on the work of Mark Boslough on
Tunguska, which was discussed in NEO News for
December 18.

David Morrison

=====================================

ASTEROID ON TRACK FOR POSSIBLE MARS HIT

By John Johnson Jr., Los Angeles Times Staff Writer
December 21, 2007

Talk about your cosmic pileups. An asteroid
similar to the one that flattened forests in
Siberia in 1908 could plow into Mars next month,
scientists said Thursday.

Researchers attached to NASA's Near-Earth Object
Program, who sometimes jokingly call themselves
the Solar System Defense Team, have been tracking
the asteroid since its discovery in late
November. The scientists, at the Jet Propulsion
Laboratory in La Cañada Flintridge, put the
chances that it will hit the Red Planet on Jan.
30 at about 1 in 75.

A 1-in-75 shot is "wildly unusual," said Steve
Chesley, an astronomer with the Near-Earth Object
office, which routinely tracks about 5,000
objects in Earth's neighborhood. "We're used to
dealing with odds like one-in-a-million," Chesley
said. "Something with a one-in-a-hundred chance
makes us sit up straight in our chairs."

The asteroid, designated 2007 WD5, is about 160
feet across, which puts it in the range of the
space rock that exploded over Siberia. That
explosion, the largest impact event in recent
history, felled 80 million trees over 830 square
miles.

The Tunguska object broke up in midair, but the
Martian atmosphere is so thin that an asteroid
would probably plummet to the surface, digging a
crater half a mile wide, Chesley said.

The impact would probably send dust high into the
atmosphere, scientists said. Depending on where
the asteroid hit, such a plume might be visible
through telescopes on Earth, Chesley said. The
Mars Reconnaissance Orbiter, which is mapping the
planet, would have a front-row seat. And NASA's
two JPL-built rovers, Opportunity and Spirit,
might be able to take pictures from the ground.

Because scientists have never observed an
asteroid impact -- the closest thing being the
1994 collision of comet Shoemaker-Levy with
Jupiter -- such a collision on Mars would produce
a "scientific bonanza," Chesley said. The
asteroid is now behind the moon, he said, so it
will be almost two weeks before observers can
plot its course more accurately.

The possibility of an impact has the Solar System
Defense Team excited. "Normally, we're rooting
against the asteroid," when it has Earth in its
cross hairs, Chesley said. "This time we're
rooting for the asteroid to hit."

==============================

ASTEROID MAY HIT MARS IN NEXT MONTH

By Alicia Chang (MSNBC & AP)

LOS ANGELES (AP) - Mars could be in for an
asteroid hit. A newly discovered hunk of space
rock has a 1 in 75 chance of slamming into the
Red Planet on Jan. 30, scientists said Thursday.

"These odds are extremely unusual. We frequently
work with really long odds when we track ...
threatening asteroids," said Steve Chesley, an
astronomer with the Near Earth Object Program at
NASA's Jet Propulsion Laboratory.

The asteroid, known as 2007 WD5, was discovered
in late November and is similar in size to an
object that hit remote central Siberia in 1908,
unleashing energy equivalent to a 15-megaton
nuclear bomb and wiping out 60 million trees.

Scientists tracking the asteroid, currently
halfway between Earth and Mars, initially put the
odds of impact at 1 in 350 but increased the
chances this week. Scientists expect the odds to
diminish again early next month after getting new
observations of the asteroid's orbit, Chesley
said. "We know that it's going to fly by Mars and
most likely going to miss, but there's a
possibility of an impact," he said.

If the asteroid does smash into Mars, it will
probably hit near the equator close to where the
rover Opportunity has been exploring the Martian
plains since 2004. The robot is not in danger
because it lies outside the impact zone. Speeding
at 8 miles a second, a collision would carve a
hole the size of the famed Meteor Crater in
Arizona.

In 1994, fragments of the comet Shoemaker-Levy 9
smacked into Jupiter, creating a series of
overlapping fireballs in space. Astronomers have
yet to witness an asteroid impact with another
planet. "Unlike an Earth impact, we're not
afraid, but we're excited," Chesley said.

===================================

SMALL ASTEROIDS POSE BIG NEW THREAT

By Charles Q. Choi, SPACE.com
19 December 2007

The infamous Tunguska explosion, which
mysteriously leveled an area of Siberian forest
nearly the size of Tokyo a century ago, might
have been caused by an impacting asteroid far
smaller than previously thought.

The fact that a relatively small asteroid could
still cause such a massive explosion suggests "we
should be making more efforts at detecting the
smaller ones than we have till now," said
researcher Mark Boslough, a physicist at Sandia
National Laboratory in Albuquerque, N.M.

The explosion near the Podkamennaya Tunguska
River on June 30, 1908, flattened some 500,000
acres (2,000 square kilometers) of Siberian
forest. Scientists calculated the Tunguska
explosion could have been roughly as strong as 10
to 20 megatons of TNT - 1,000 times more powerful
than the atom bomb dropped on Hiroshima.

Wild theories have been bandied about for a
century regarding what caused the Tunguska
explosion, including a UFO crash, antimatter, a
black hole and famed inventor Nikola Tesla's
"death ray." In the last decade, researchers have
conjectured the event was triggered by an
asteroid exploding in Earth's atmosphere that was
roughly 100 feet wide (30 meters) and 560,000
metric tons in mass - more than 10 times that of
the Titanic.

The space rock is thought to have blown up above
the surface, only fragments possibly striking the
ground.

Now new supercomputer simulations suggest "the
asteroid that caused the extensive damage was
much smaller than we had thought," Boslough said.
Specifically, he and his colleagues say it would
have been a factor of three or four smaller in
mass and perhaps 65 feet (20 meters) in diameter.

The simulations run on Sandia's Red Storm
supercomputer - the third fastest in the world -
detail how an asteroid that explodes as it runs
into Earth's atmosphere will generate a
supersonic jet of expanding superheated gas. This
fireball would have caused blast waves that were
stronger at the surface than previously thought.

At the same time, previous estimates seem to have
overstated the devastation the event caused. The
forest back then was not healthy, according to
foresters, "and it doesn't take as much energy to
blow down a diseased tree than a healthy tree,"
Boslough said. In addition, the winds from the
explosion would naturally get amplified above
ridgelines, making the explosion seem more
powerful than it actually was. What scientists
had thought to be an explosion between 10 and 20
megatons was more likely only three to five
megatons, he explained.

All in all, the researchers suggest that smaller
asteroids may pose a greater danger than
previously believed. Moreover, "there are a lot
more objects that size," Boslough told SPACE.com.

NASA Ames Research Center planetary scientist and
astrobiologist David Morrison, who did not
participate in this study, said, "If he's right,
we can expect more Tunguska-sized explosions -
perhaps every couple of centuries instead of
every millennia or two." He added, "It raises the
bar in the long term - ultimately, we'd like to
have a survey system that can detect things this
small."

Boslough and his colleagues detailed their
findings at the American Geophysical Union
meeting in San Francisco on Dec. 11. A paper on
the phenomenon has been accepted for publication
in the International Journal of Impact
Engineering.

--
+++++++++++++++++++++++++++++++++++++++++++

NEO News (now in its fourteenth year of
distribution) is an informal compilation of news
and opinion dealing with Near Earth Objects
(NEOs) and their impacts. These opinions are the
responsibility of the individual authors and do
not represent the positions of NASA, Ames
Research Center, the International Astronomical
Union, or any other organization. To subscribe
(or unsubscribe) contact dmorrison@xxxxxxxxxxxxx
For additional information, please see the
website http://impact.arc.nasa.gov. If anyone
wishes to copy or redistribute original material
from these notes, fully or in part, please
include this disclaimer.







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[FMO] Asteroid to hit Mars (Fwd: NEO News (12/21/07) "Tunguska" on Mars?)

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