Daily News Magazine from India & around the world.

THE LIST of discoveries made by India’s maiden lunar mission, Chandrayaan, is growing. The latest addition is the presence of a mini- magnetic field on the lunar surface.

Analysis of data beamed back by one of the 11 payloads carried by the lunar orbiter, SARA ( Sub- keV Atom Reflecting Analyser), shows the presence of a mini- magnetosphere on the lunar surface. This is the first direct evidence of some sort of a localised magnetic field present on the moon.

“ The magnetosphere, which indicates the presence of a magnetic field, observed is localised in an area near the Gerasimovic crater, but there could be more such minimagnetospheres on the moon’s surface,” said Dr Anil Bhardwaj, head of planetary science at the Vikram Sarabhai Space Centre, Trivananthapuram, which had jointly conducted the experiment with the Swedish Institute of Space Physics.

The magnetosphere has a diameter of about 360 km and is surrounded by a ringshaped region about 300 km wide. The observations by SARA were made on June 17, 2009 when Chandrayaan was orbiting the moon from an altitude of just 200 km above the lunar surface.

Unlike the earth, the moon does not have a global magnetic field and, therefore, does not have a magnetosphere surrounding it. The magnetic field of the earth is surrounded by the magnetosphere, which keeps most of the particles from the sun, carried in solar wind, from hit- ting the earth and makes the planet’s atmosphere livable.

It was so far believed that the moon has small regions of magnetisation called magnetic anomalies. These small areas of locally strong magnetic fields can create minimagnetospheres that deflect the solar wind in the same way the earth’s magnetosphere shields most of the planet from solar wind.

But these were only theories, there was no clear cut evidence.

Now Chandrayaan has provided direct proof of the magnetosphere on the moon.

The study has been published in scientific journal Geophysical Research Letters . Solar wind, a constant stream of particles given off by the sun, contains largely protons. They collide with every celestial object in the solar system but are usually stopped by the object’s atmosphere. On bodies without such a natural shield, for example asteroids or the planet Mercury, solar wind reaches the ground.

When these protons from the solar wind hit the surface of the moon, some are scattered back as energetic neutral hydrogen atoms.

Using data from SARA, researchers identified a region above a strong magnetic anomaly where the number of energetic hydrogen atoms bouncing back was lower than in surrounding areas, Bhardwaj said.

This indicates that the region was shielded by a minimagnetosphere, as protons were getting deflected along the flanks of the magnetic shield.