[meteorite-list] ESO Views of Earth-Approaching Asteroid Toutatis

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Sep 29 15:19:17 2004
Message-ID: <200409291815.LAA08825_at_zagami.jpl.nasa.gov>

ESO Education and Public Relations Dept.

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Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/outreach/press-rel/pr-2004/phot-28-04.html
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For immediate release: 29 September 2004

ESO Press Photos 28a-e/04

ESO Views of Earth-Approaching Asteroid Toutatis

Unique Photos from La Silla and Paranal Measure the Distance

   ESO PR Photo 28a/04 ESO PR Photo 28b/04

   Asteroid Toutatis with the Asteroid Toutatis' Long Trail
   VLT

   Caption: ESO PR Photos 28a-b/04 show the Earth-approaching
   asteroid (4179) Toutatis, as photographed with the FORS1
   multimode instrument at the 8.2-m VLT Kueyen telescope at
   the ESO Paranal Observatory. At the time of these exposures,
   the asteroid was about 1,640,000 km from the Earth and
   moving rapidly across the sky in the southern constellation
   Ara (The Altar). In PR Photo 28a/04, the telescope was set
   to follow the predicted motion of the asteroid during 60
   seconds (beginning on September 28, 2004, 23:34 hrs UT) and
   the images of the background stars in the sky field
   therefore appear as long trails. In PR Photo 28b/04
   (beginning on September 28, 2004, 23:46 hrs UT), the
   exposure time was 5 min while the telescope was following
   the normal diurnal motion; the stars now appear as points
   of light, while the asteroid's long trail crosses the entire
   field-of-view. Both photos were obtained through a narrow
   optical filter.

Today, September 29, 2004, is undisputedly the Day of
Toutatis, the famous "doomsday" asteroid.

Not since the year 1353 did this impressive "space rock" pass
so close by the Earth as it does today. Visible as a fast-
moving faint point of light in the southern skies, it
approaches the Earth to within 1,550,000 km, or just four
times the distance of the Moon.

Closely watched by astronomers since its discovery in January
1989, this asteroid has been found to move in an orbit that
brings it close to the Earth at regular intervals, about once
every four years. This happened in 1992, 1996, 2000 and now
again in 2004.

Radar observations during these passages have shown that
Toutatis has an elongated shape, measuring about 4.6 x 2.4 x
1.9 km. It tumbles slowly through space, with a rotation
period of 5.4 days.

The above images of Toutatis were taken with the ESO Very
Large Telescope (during a technical test) in the evening of
September 28. They were obtained just over 12 hours before
the closest approach that happens today at about 15:40 hrs
Central European Summer Time (CEST), or 13:40 hrs Universal
Time (UT). At the time of these observations, Toutatis was
about 1,640,000 km from the Earth, moving with a speed of
about 11 km/sec relative to our planet.

They show the asteroid as a fast-moving object of magnitude
10, about 40 times fainter than what can be perceived with
the unaided, dark-adapted eye. They also prove that Toutatis
is right on track, following exactly the predicted trajectory
in space and passing the Earth at a safe distance, as
foreseen.

Detailed calculations, taking into account all available
observations of this celestial body, have shown that although
Toutatis passes regularly near the Earth, today's passage is
the closest one for quite some time, at least until the year
2562. The ESO observations, obtained at a moment when Toutatis
was very close to the Earth, will help to further refine the
orbital calculations.

The "parallax effect" demonstrated!

   ESO PR Photo 28c/04 ESO PR Photo 28d/04

   Asteroid Toutatis from Asteroid Toutatis from La
   Paranal Silla

   ESO PR Photo 28e/04

   The Parallax of Asteroid Toutatis

   Caption: ESO PR Photo 28e/04 is a composite, false-colour
   image showing asteroid (4179) Toutatis moving in front of
   background stars, as seen from Paranal (red trail) and La
   Silla (green trail). The two photos used for this
   combination are shown as PR Photos 28c-d/04; they were
   obtained nearly simultaneously in the morning of September
   29, at 02:30 hrs UT, when the asteroid was passing through
   the constellation of Triangulum Australe ("The Southern
   Triangle"). The offset between the two trails corresponds
   to the difference of the lines-of-sight from the two
   telescopes towards the object. Two 1-min images were taken
   almost simultaneously with the FORS-1 instrument on Kueyen,
   the second 8.2m VLT Unit Telescope on Paranal, and on the
   WFI camera installed on the ESO/MPI 2.2m telescope at La
   Silla. The WFI image was obtained though a R broad-band
   filter; on the VLT, a narrow band [O III] interference
   filter was used to attenuate the light of the bright
   asteroid. The images were then scaled and processed in order
   to compensate for the different characteristics of the two
   instruments (scale, orientation, distortion, sensitivity).
   The VLT image is displayed in red, the WFI image in green.
   As the stars are common to both images, they appear
   yellowish.

Simultaneous images obtained with telescopes at ESO's two
observatories at La Silla and Paranal demonstrate the
closeness of Toutatis to the Earth. As can be seen on the
unique ESO PR Photo 28e/04 that combines two of the exposures
from the two observatories, the sighting angle to Toutatis
from the two observatories, 513 km km apart, is quite
different. Astronomers refer to this effect as the "parallax".
The closer the object is, the larger is the effect, i.e., the
larger will be the shift of the line-of-sight.

Interestingly, the measured angular distance in the sky of
the beginnings (or the ends) of the two trails (about 40
arcsec), together with the known distance between the two
observatories and the position of Toutatis in the sky at the
moment of the exposures fully define the triangle "Paranal-
Toutatis-La Silla" and thus allow to calculate the exact
distance to the asteroid.

It is found to be very close to that predicted from the
asteroid's position in its orbit and that of the Earth at
the moment of this unique observation, 1,607,900 km. This
exceptional, simultaneous set of observations thus provides
an independent measurement of Toutatis' distance in space
and, like the measured positions, a confirmation of its
computed orbit.

More information about Toutatis is available at the dedicated
webpage by the French discoverers and also at the specialised
Near-Earth Objects - Dynamic Site.
Received on Wed 29 Sep 2004 02:15:28 PM PDT