Comet Collision to Come?

Trail of crumbs discovered from potentially hazardous comet –
could February 4 be a future doomsday?



This +2 magnitude February eta Draconid was filmed by Peter Jenniskens with one of the low-light-level video cameras of the Cameras for Allsky Meteor Surveillance (CAMS) station in Mountain View, California, at 07:59:24 UT on February 4, 2011. Credit: CAMS/SETI

A telegram was issued on July 10th by the Central Bureau for
Astronomical Telegrams of the International Astronomical Union
announcing that the Earth got impacted for a few hours by a stream of
dust from a potentially dangerous comet last February 4.



"This particular shower happens only once or twice every sixty years,"
says discoverer Dr. Peter Jenniskens of the SETI Institute and NASA
Ames. "The stream of dust is always there, but quite invisible just
outside of Earth´s orbit. Only when the planets steer the dust in
Earth´s path do we get to know it is there."



Jenniskens heads the Cameras for Allsky Meteor Surveillance (CAMS)
project in California. Since last October, the SETI Institute has
teamed up with Fremont Peak Observatory and UCO/Lick Observatory in
monitoring the night sky with low-light video cameras in an effort to
map the meteor showers in the sky over the San Francisco Bay Area.
They triangulate the meteor trajectories and determine their orbit in
space.



The International Astronomical Union keeps score of showers that were
claimed to exist in the past and now has a list of 300+ showers that
need confirmation. Only 64 showers have been established so far.
Jenniskens´ goal is to establish many more.



While reducing the Fremont Peak and Mountain View station observations
from February 4, normally a night with not much going for it,
Jenniskens discovered a handful of meteoroids that arrived at Earth
from the exact same direction in the sky. The meteoroids arrived from
the direction of the star Eta Draconis, and the shower is now
recognized by the International Astronomical Union as the February Eta
Draconids (FEDs for short). This was the first new shower discovered
in the CAMS project, and a very unusual one at that.



The meteoroids in question were moving on a very elongated orbit,
typical of that of long-period comets such as Hale-Bopp. Unlike
Hale-Bopp, this one passes close to Earth´s orbit. Long-period comets
come back to the Sun only rarely and if any one is on a trajectory to
hit the Earth, we could have little warning.



The meteoroids were moving on a very elongated orbit, typical of long-period comets like Hale-Bopp (pictured above). Image Credit: Philipp Salzgeber

Now, Jenniskens has found the trail of crumbs of such a comet, which
passed very close to Earth´s orbit the last time it was near the Sun.
That could have been only a few hundred years ago, or many thousands.
At that time, the comet released a cloud of dust which is now
returning. Some dust grains return earlier than others, depending on
how elongated their orbit ended up being, and the result is a
continuous stream of returning dust grains. That stream is detected
only when it encounters the Earth, when the meteoroids cause a brief
2-hour meteor shower.



"Earth gets hosed typically only once or twice every sixty years by
such streams," says Jenniskens. "Only when Jupiter and Saturn are back
at their original positions do they steer the dust trail in our path.
The trail wags in and out of Earth´s path much like the Sun moves
around in response to the motion of these heavy planets."



The February Eta Draconids follow a short list of other such known
showers, which include the November 22 Alpha Monocerotids, which were
seen last in 1995, and the September 1 Aurigids, which created a
spectacular shower in 2007. The return of those showers was predicted
by Jenniskens.



Now the February Eta Draconid shower has been discovered, Jenniskens
is confident that a next return can be predicted. He teamed with
Finnish astronomer Esko Lyytinen to investigate. Lyytinen calculated a
possible return in 2016 or 2023, after that not again until 2076.



Future observations of this shower may pry loose other information
about the comet that caused this stream of meteoroids, which is a
potential danger to Earth.
"If the meteoroids can hit us, so can the
comet," says Jenniskens, "We don´t know whether the comet has already
passed us by or is still on approach."
To get some extra advance
warning, one could look along the measured orbit to those spots where
the comet could arrive at Earth´s orbit on a future February 4 date.



"Even then, chances are very small that the comet will actually hit
us, as such impacts are rare in Earth´s history," he added.