Last Monday, Valentine's Day, NASA's NEAR satellite achieved a notable 'first' when it entered orbit around a near-Earth asteroid named 433 Eros. While this romantic rendezvous should provide a host of new information about the potato-shaped little world, Eros is just one out of many millions of asteroids roaming the Solar System.

Further insights into the nature of these ancient rocks will be gained later this decade when ESA's Rosetta spacecraft encounters two contrasting asteroids which inhabit the main asteroid belt between Mars and Jupiter.

Apart from the nine planets, our Solar System contains a multitude of minor planets, officially known as asteroids. Once known as the 'vermin of the skies,' scientists now recognise that these battered chunks of rock contain important clues to the events that took place during the formation of the Solar System. However, despite a handful of asteroid flybys by spacecraft during the 1990's, many mysteries still remain.

One difficulty is that the asteroids are not all made of the same material. Some are stony, some are rich in iron and others seem to contain large amounts of carbon. Most of the asteroids so far visited by spacecraft have been of the stony type (including Eros). Apart from Mathilde, a coal-black object which is not much denser than water, little is known about the other asteroid types.

Rosetta will be able to clear up some of the mystery during its eight year odyssey to Comet Wirtanen. As the spacecraft swings around the inner Solar System, it will make two trips across the main asteroid belt, enabling it to examine two very different asteroids, 140 Siwa and 4979 Otawara.

The asteroids to be visited by Rosetta are two very contrasting objects. Siwa will be the largest asteroid ever encountered by a spacecraft, while (apart from a tiny asteroid moon called Dactyl), Otawara will be the smallest.

Rosetta's flyby of Otawara will take place on 11 July, 2006, when the asteroid is 1.89 AU (1.89 times the Earth's distance) from the Sun. Travelling at a relative velocity of 10.63 km/sec, the spacecraft will pass by Otawara's sunlit side at a distance of about 1595 km.

Apart from its orbit, very little was known about Otawara until recent ground-based studies were undertaken in order to learn more about its physical and chemical make-up. Observations were obtained during an international campaign using telescopes in France, Chile and the USA.

Otawara is likely to be a stony object rich in the minerals pyroxene and/or olivine. However, it may be a member of the asteroid family named after its largest member, 4 Vesta. Assuming that the asteroid is quite dark, its diameter is probably only 2.6 - 4 km. Its density is uncertain, but is probably 2 - 2.5 times greater than water (i.e. twice the density of Mathilde).

Studies of changes in its reflected light -- its light curve -- indicate that Otawara rotates quite quickly, once every 2.7 hours. This is faster than any asteroid so far visited by spacecraft. Such rapid spin will be an advantage during Rosetta's flyby, enabling its instruments to image and measure the asteroid's characteristics at high resolution during one complete rotation.

With a diameter of around 110 km, Siwa is much larger than any asteroid so far examined by spacecraft. Spectral studies indicate that it is a very black, primitive, carbon-rich object which has probably been less altered by collisions than its smaller cousins. Figures for its rotation period vary between 18.5 hours and 22 hours.

Rosetta will obtain spectacular images and high resolution data as it flies to within 3,000 km of Siwa on 24 July 2008. The spacecraft will fly past at a velocity of 17.04 km/sec, approaching the sunlit side and looking at a crescent phase as it moves away. At this time, Siwa will be at 2.75 AU from the Sun and 3.11 AU from the Earth, so signals from the spacecraft will take 26 minutes to reach ground stations.

Following these short-lived encounters, Rosetta will travel beyond the asteroid belt before closing in on another of the Solar System's smaller inhabitants -- Comet Wirtanen. It will then complete an historic double by entering orbit around the comet's nucleus and deploying a lander on its icy surface.

ITHACA, N.Y. -- NASA has given the go-ahead for the Cornell University-led Comet Nucleus Tour, or Contour, mission. The agency said the mission has passed a critical review and the building of the spacecraft can begin.

Cornell will lead and direct the $158 million mission to conduct close-proximity comet flybys. The spacecraft is scheduled for launch in July 2002, with the precise launch date to be decided in the next year or two.

The principal investigator on the mission is Joseph Veverka, professor of astronomy at Cornell and chair of the astronomy department. Other Cornell researchers on the team are Steven W. Squyres, professor of astronomy, who will interpret the geology of the comets; James Bell, assistant professor of astronomy, who will interpret the spectral maps of the comets; and Peter C. Thomas, senior research associate, who is a leading expert in determining the size and shape of irregular objects like comets.

David Jarrett of NASA's Discovery Program, said, "After successful completion of both the preliminary design review and an independent confirmation assessment, the Contour team is well on its way toward completing the spacecraft design."

The launching of Contour is timed to encounter and study Comet Encke in November 2003 and Comet Schwassmann-Wachmann-3 in June 2006. The mission has the flexibility to include a flyby of Comet d'Arrest in 2008 or to retarget itself to approach an unforeseen cometary visitor to the inner solar system. Mission scientists are hopeful they will have the opportunity to study a newly discovered comet, such as Comet Hale-Bopp, which was discovered by amateur astronomers in 1995.

The spacecraft, to be launched aboard a Delta rocket, will be outfitted with a solar array for power and a high-gain antenna for communication with Earth. The Contour spacecraft will venture about 30 million miles from Earth to study the comets. Building of the spacecraft at the Applied Physics Laboratory at Johns Hopkins University, which is managing the mission, begins this month.

The nucleus of a comet is its heart, believed by scientists to be a tiny, irregular chunk of ice and rock. To date only one comet nucleus has ever been viewed with a spacecraft: Comet Halley in 1986. The spacecraft will fly past at least two comets and take far better pictures than those of Halley. It will also collect and analyze dust to reveal the comet's makeup, greatly improving our knowledge of key characteristics of comet nuclei and providing an assessment of their diversity.

The mission also will clear up the many mysteries of how comets evolve as they approach the Sun and their ices begin to evaporate.

The spacecraft will fly by each comet at the peak of its activity, close to the Sun. During each encounter, the target comet will also be well situated in the night sky for astronomers worldwide to make concurrent observations from the ground. The spacecraft will fly by each comet at a distance of about 100 kilometers (62 miles).

Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.

This morning NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft became the first space probe to orbit an asteroid and quickly began sending close-up pictures of 433 Eros back to Earth.

"This is what we are in this business for", enthused NASA associate administrator Carl Pincher. "This is a grand day."

"It's like Christmas for us," agreed Cornell University's Prof. Joe Veverka, the leader of NEAR's imaging team. Veverka was clearly anxious to return to the incoming data as he gamely answered questions throughout an hour-long press conference at Johns Hopkins University.

Just over an hour after entering orbit around Eros, NEAR pointed its camera at the asteroid and took a picture from a range of 210 miles (330 km) above the surface. It shows the 3-mile (5-kilometer) impact crater which the spacecraft has spied for over a week during its approach. The two smaller craters superimposed on its rim are each about 1.2 miles (2 kilometers) across. This crater doesn't yet have a name, but eventually it will be given one by the International Astronomical Union. The theme for naming craters on Eros will be love and lovers, according to NEAR project scientist Andrew Cheng.

Today's high resolution image shows features as small as a 100 feet (30 meters) across.

"The picture shows evidence of layering and other structures, like grooves and rims. There's a lot of geologic complexity. Global structures like grooves suggest severe collisions. It looks like Eros will turn out to be an extremely interesting object!" said Prof. Veverka.

CAMBRIDGE, MA -- Anxious astronomers, uncertain whether to run for cover or to tool up their telescopes, now at least will get their needed answers faster, thanks to a new high-speed computer at the world's asteroid and comet early-alert center.

A grant from the Tamkin Foundation of Los Angeles, CA, has permitted the creation of a high-speed computer network for the Minor Planet Center, the international clearing house for astronomical information based at the Smithsonian Astrophysical Observatory (SAO), that will allow more rapid determination of the paths of newly discovered asteroids and comets, including those on possible crash courses with Earth.

The Minor Planet Center, operated for the International Astronomical Union, serves the world scientific community by collecting, checking, and disseminating positional observations and orbital data for asteroids and comets. Tracking many thousands of objects simultaneously, the Center distributes initial and updated data by means of the Minor Planet Electronic Circulars (issued via email several times a day) and monthly consolidations of the data in the printed Minor Planet Circulars. The new "Tamkin Foundation Computing Network" will greatly enhance the level of service the Center can provide to astronomers around the world.

Steven M. Tamkin, Executive Vice-President, presented his family foundation's contribution to Irwin I. Shapiro, Director of SAO, at an informal ceremony in Cambridge recently.

An amateur astronomer with a deep interest in near-Earth asteroids and other objects with the potential to collide with the Earth, Mr. Tamkin noted that "This is the Foundation's first investment in nonmedical scientific research, and we look forward to a long and fruitful partnership in supporting the Center's work."

The combination of observational and computational research is vital in astronomy, according to Brian Marsden, the Director of the Center and Associate Director of SAO's Planetary Sciences Division. "During the past few years new technology has completely revolutionized the way astronomers make their observations," says Marsden.

"At numerous observatories around the world, computer programs examine an electronic image of the sky, immediately reduce the data for each asteroid or comet to a string of numbers, and then communicate those numbers to us at the Minor Planet Center," he says.

"Our computer programs automatically establish which observations belong to the same asteroid or comet and make successive improvements to the orbital solutions that are then added to the database used to identify further observations," Marsden explains. "It is very rewarding for us that the Tamkin Foundation will support the computing technology that is integral to this kind of research."

The Minor Planet center currently keeps tabs on the orbits of some 57,000 asteroids and 1,050 comets. In 1999 alone, there have so far been 25,000 new asteroids and 60 comets discovered.

In his thanks, SAO Director Irwin Shapiro praised the Tamkin Foundation's willingness to branch out into new areas of scientific inquiry.

At 11:00 a.m. Eastern time, navigation data from the Near Earth Asteroid Rendezvous spacecraft indicates NEAR has achieved orbit around asteroid 433 Eros.

At 10:33 a.m., with Eros about 203 miles (327 kilometers) below, NEAR's small hydrazine thrusters fired for 57 seconds, slowing the spacecraft's approach to walking speed and easing it into the asteroid's weak gravitational pull. The rendezvous took place about 160 million miles (256 million kilometers) from Earth.

"NEAR is now the first spacecraft to successfully lock into orbit around an asteroid," says Mission Director Dr. Robert Farquhar, from the NEAR Mission Operations Center at the Applied Physics Laboratory in Laurel, Md. "We're making history here today."

Over the next 24 hours, instrument data and pictures of the asteroid taken after the orbit insertion burn will provide more details about NEAR's precise position around Eros. The first orbit images from NEAR are expected this afternoon.

For more information about the NEAR mission, see the recent SpaceScience.com headline "Eros or Bust" and the NEAR Mission Home Page from Johns Hopkins University.