CCNet 62/2003 - 2 September 2003
--------------------------------
Today both risk monitors downgraded their overall risk assessments for this
object, with NEODyS dropping its impact solution count by one and no longer
having any solutions rated above Torino Scale 0 (TS-0). JPL, however, added
and removed impact solutions for a net gain of two (31 total in the years
2014-2099), and still rates its solution for 21 March 2014 at TS-1 ("merits
special monitoring").
--Asteroid/Comet Connection, 1 September 2003
As far as the public is concerned, it just isn't worth getting worried about
an object with a couple weeks of optical data showing a possible Earth
encounter years from now. Sometimes, it can't even be said for certain what
side of the Sun such an object will be on at the time of the listed possible
impact. A few days later, additional measurements will shrink the orbit
uncertainty region by a relatively large amount and the Earth will fall out
of the risk zone.
--Jon Giorgini, Jet Propulsion Laboratory, CCNet - 26 July 2002
(1) ASTEROID IMPACT RISK DOWNGRADED
(2) POTENTIALLY HAZARDOUS ASTEROID GIVEN TORINO 1 RATING
(3) ASTEROID WARNING FOR 2014
(4) THE MEANING OF ASTEROID RISK LISTINGS
================
(1) ASTEROID IMPACT RISK DOWNGRADED
Asteroid/Comet Connection, 1 September 2003
http://www.hohmanntransfer.com/news.htm
The Sunday DOU carries observations of 2003 QQ47 overnight by Sormano and
Great Shefford observatories. Today both risk monitors downgraded their overall
risk assessments for this object, with NEODyS
(http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:2003QQ47;risk)
dropping its impact solution count by one and no longer having any solutions
rated above Torino Scale 0 (TS-0). JPL
(http://neo.jpl.nasa.gov/risk/2003qq47.html), however, added and removed
impact solutions for a net gain of two (31 total in the years 2014-2099), and
still rates its solution for 21 March 2014 at TS-1 ("merits special monitoring").
NEODyS continues to show two impact solutions in 2076 and JPL one, but both
have now significantly lowered their risk ratings for that year, which at
different times they had independently rated at TS-1. Such assessments are
ephemeral and of no importance once superceded with newer data and analysis,
but they do help demonstrate the routine cycle of observation and calculation
used to discover and eliminate risk concerns.
Copyright 2003, Asteroid/Comet Connection
===============
(2) "POTENTIALLY HAZARDOUS ASTEROID GIVEN TORINO 1 RATING"
NEO Information Centre, 2 September 2003
http://www.nearearthobjects.co.uk/news_display.cfm?code=news_intro&itemID=196
A potential asteroid impact on 21 March 2014 has been given a Torino hazard
rating of 1, defined as 'an event meriting careful monitoring'. The newly
discovered 1.2 km wide asteroid, known to scientists as 2003 QQ47, has a mass
of around 2 600 billion kg, and would deliver around 350 000 MT of energy in
an impact with Earth. Currently, the overall probability of this asteroid
impacting Earth is 1 in 909 000. However, the orbit calculations are based on
just 51 observations during a 7-day period. Dr Alan Fitzsimmons of Queen's
University, Belfast, one of the expert team advising the UK NEO information
Centre said "The NEO will be observable from Earth for the next 2 months, and
astronomers will continue to track it over this period."
Lincoln Near Earth Asteroid Research Program (LINEAR), operating out of
Socorro, New Mexico, first observed the giant rock on 24 August and reported
their observations to the Minor Planet Centre in Massachusetts. The Minor
Planet Centre plays a crucial role as the clearinghouse for all new
discoveries of asteroids and comets. "As additional observations are made
over the coming months, and the uncertainties decrease, asteroid 2003 QQ47
is likely to drop down the Torino scale," said Kevin Yates, project manager
for the UK NEO Information Centre, based at the National Space Centre in
Leicester. "The NEO Information Centre will continue to monitor the latest
results of observations and publish regular updates on our website."
Asteroids such as 2003 QQ47 are chunks of rock left over from the formation of
our Solar System 4.5 billion years ago. Most are kept at a safe distance from
Earth in the asteroid belt between the orbits of Mars and Jupiter. However,
the gravitational influence of giant planets such as Jupiter can nudge
asteroids out of these safe orbits and send them plunging into the Earth's
neighbourhood.
===============
(3) "ASTEROID WARNING FOR 2014"
BBC News Online, 2 September 2003
http://news.bbc.co.uk/1/hi/uk/3200019.stm
The British agency responsible for identifying potentially hazardous asteroids
says US astronomers are warning of a possible collision in 2014.
The UK Government's Near Earth Object Centre says American astronomers have
discovered a large, fast-approaching asteroid that could hit the Earth on
21 March, 2014.
But they add the chances of it doing so are just one in 909,000.
What is more, any risk of an impact is likely to decrease as further data is
gathered, they say.
Credible threat
The BBC's science correspondent Christine McGourty says that, although the
chances this asteroid will hit the Earth are slim, it is considered worth
monitoring due to its sheer size and velocity.
The rock is said to measure approximately two thirds of a mile across - only
one tenth of the size of the meteor thought to have wiped out the dinosaurs
65 million years ago.
It is travelling at a speed of about 20 miles per second.
"In theory such an asteroid could cause devastation across an entire
continent," Christine McGourty says.
It has been labelled "2003 QQ 47" and astronomers will be monitoring it
closely for the next two months.
Copyright 2003, BBC
================
(4) THE MEANING OF ASTEROID RISK LISTINGS
CCNet, 26 July 2002
http://abob.libs.uga.edu/bobk/ccc/cc072602.html
Jon Giorgini
Dear Benny,
Based on discussions with the press and others in the wake of 2002 NT7, it
seems NONE of the people I have talked to (no one outside the "impact
community") understands the meaning of a listing on a risk page. That is,
the difference between the "potential impacts" and "predicted impacts".
Two or three weeks of optical data is not enough to conclusively identify an
impact years in the future. POSSIBLE hazards can be flagged, but these are
actually due to the lack of orbit knowledge; the asteroid could be so many
places the Earth can't help but be in some of them.
These listings are POSSIBLE impacts, not PREDICTED impacts.
To PREDICT an asteroid's orbit reliably you need radar measurements or at
least optical observations spanning 1 (preferably two) orbit periods of the
asteroid. With an orbit period of 2.29 years, that means we should be able
to usefully predict 2002 NT7's orbit in a positive way for a few decades
after 2-4 more years of tracking it. By contrast, eliminating an entry on
the risk page is a negative prediction; a prediction of where it will NOT be.
Results with less data -- 2 or 3 weeks or even months -- are simply
astronomer's doing their routine, daily chore of eliminating obscure
possibilities.
The listings are not really PREDICTIONS of impact, but a statement that one
is POSSIBLE, primarily because it is not known for sure where the asteroid
will be. Of course lots, of things are possible, most of which will not happen.
It's possible I will be on top of Mount Everest next month but I am not
predicting it. And there will come a point when my being on Mount Everest at
some instant can be positively excluded ("that's impossible!").
The purpose behind the risk web page JPL produces is to communicate
possibilities to other astronomers so they know which objects require more
observations. A listing is not a declaration that an object is predicted to
impact, or even come close to the Earth at that time, only that the
possibility has not been ruled out.
As far as the public is concerned, it just isn't worth getting worked up over
an object with a couple weeks of optical data showing a possible Earth
encounter years from now. SOMETIMES, IT CAN'T EVEN BE SAID FOR CERTAIN WHAT
SIDE OF THE SUN SUCH AN OBJECT WILL BE ON AT THE TIME OF THE
LISTED POSSIBLE IMPACT. A few days later, additional measurements will shrink
the orbit uncertainty region by a relatively large amount and the Earth will
fall out of the risk zone.
A pointer to such objects is valuable to astronomers however, so they can
organize their limited resources to continuing tracking objects with
POSSIBLE (but by no means PREDICTED) impact potential.
In general, it is very difficult for fuzzy optical measurements to narrow the
uncertainties for newly discovered objects. A conclusive impact detection will
almost certainly have to come from radar which can measure the position of an
object to within a few meters. Optical measurements
are typically good only at the 10's-100's of km level which fuzzes out
knowledge quickly in a few years.
The only substantive hazard prediction out there is 1950 DA; 51 years of
optical data and recent radar data together indicate a possible impact event
with odds between 0 and 1-in-300 on March 16, 2880. Ground-based observers
could track 1950 DA for the next few decades without substantially changing
the possibilities since the orbit uncertainties are so small they are
dominated by the way the asteroid spins in space.
Regards,
Jon Giorgini |Navigation & Mission Design Section
Senior Engineer | Solar System Dynamics Group
Jon.Giorgini@jpl.nasa.gov | Jet Propulsion Laboratory
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