What's new since Valentine's Day?

Do you remember anything special happening this last Valentine's Day? I'm not talking about a nice flower, a precious gift or a love letter you received from a beloved one... It is something which happened far away, somewhere in our solar system more than 270 million miles from the Earth... It made the news, and then fell into oblivion. However, since this Valentine's Day, it is astounding scientists with incredible pictures and invaluable data. Still puzzled? At 10:33 AM EST on that Valentine Day, a spacecraft was successfully inserted into orbit around 433 Eros.

433 Eros, named after the god of love in the Greek mythology, is an asteroid discovered photographically by Gustav Witt, director of the Urania Observatory in Berlin, Germany, on Saturday night, August 13, 1898. All the asteroids know at that time were orbiting between Mars and Jupiter, in what we called the Main Belt. Eros however appeared to orbit mainly between the Earth and Mars, coming as close to the Earth as 14 million miles! Since then, many asteroids coming close to the Earth, or near-Earth asteroids, have been found, but Eros accounts for nearly half the volume of all of them.

The NEAR (Near-Earth Asteroid Rendezvous) spacecraft is launched on Feb. 17, 1996 from Cape Canaveral on a Delta-2 rocket. Its main mission is to answer fundamental questions about the nature of the near-Earth objects. You know that some of them can really come very close, and that in the past many of them have actually hit the Earth. The impacts of the largest ones are devastating, and could be the cause of mass extinctions of many living species like the dinosaurs. Nearly three years after its launch, the NEAR spacecraft reaches Eros, but its initial rendezvous maneuver aborts on Dec. 20, 1998 moments after thruster firing starts. The spacecraft is found healthy when communications are resumed after the incident, and an alternate route is planned for another rendezvous more than a year later, on Valentine's Day 2000.

How does Eros look like? Forget about the Earth and the Moon, which look like nearly spherical bodies. Eros has a very irregular shape, closer to a potato than to a ball, as you can see on the series of shots taken while NEAR was approaching its target. It's not big, only 21 miles (33 kilometers) long, 8 miles (13 kilometers) wide, about the size of Molokai, and 8 miles thick. Its surface is mainly full of craters of various sizes. When you read these lines, the spacecraft is descending toward a 62-mile (100-kilometer) orbit, which will be reached on April 11. In May, NEAR should orbit even closer at an altitude of only 31 miles (50 kilometers)...

NEAR is equipped with five instruments, which are observing Eros in order to determine its shape and surface features, to map mineral distributions and abundance (images in different colors and spectra in the near infrared), to build up high resolution topographic profiles and provide a global shape model of Eros (laser altimeter), to detect elements on the surface (X-Ray and Gamma-Ray spectrometers), and finally to search for and map any intrinsic magnetic field around Eros. NEAR has been orbiting Eros on a nearly circular orbit for a month at an altitude of 124 miles (200 kilometers). Even if the mission is only in its very early phase (it should end on Valentine's Day 2001), amazing results have already been obtained. The mapping of the surface shows areas with only a few craters, an indication that the surface went through some process at a later phase than the craterisation (thought to be rather old). These geologic phenomena could have originated on a much larger parent body from which Eros was derived. Ridges, chains of craters, and boulders are surprisingly abundant, as you can see on the close-up. In addition to these images, NEAR's first X-ray detection of Eros demonstrated the presence of magnesium, iron, and silicon and possibly aluminum and calcium, and the laser altimeter has provided its first results!

When you read these lines, the spacecraft is descending toward a 62-mile (100-kilometer) orbit, which will be reached on April 11. In May, NEAR should orbit even closer at an altitude of only 31 miles (50 kilometers). More news on the mission... this Summer!

Eros is seen rotating on itself while NEAR is approaching its rendezvous. Eros rotates once every 5 hours and 16 minutes. It looks like a potato 21 miles long and 8 miles thick. 
Photo credit NASA/JHUAPL.

A detail of Eros' north polar region, as seen by NEAR from a range of 206 kilometers (127 miles). The area shown in the image is 10 kilometers (6.2 miles) across. Most of the north polar region is heavily cratered but the region to the left has a lower crater density, indicating that the surface has been modified since it first formed.
Photo credit NASA/JHUAPL

Christian Veillet
Canada-France-Hawaii Telescope