April 9, 2009

Earthshine confirmed on moon’s far side

An Australian-led study shows, for the first time, differences in light reflection from Earth's land masses and oceans can be seen on the moon's far side.

The researchers, led by Sally Langford of the University of Melbourne and including scientists from Princeton University, said the phenomenon, known as earthshine, might be used to view the physical makeup of planets too small to allow an image to be made of their surface.

Langford said the brightness of the reflected earthshine varied as the Earth rotated, revealing the difference between the intense mirror-like reflections of the ocean compared with the dimmer land.

The three-year study was conducted so that in the evening, when the moon was a waxing crescent, the reflected earthshine originated from Indian Ocean and Africa's east coast. In the morning, when the moon was a waning crescent, it originated only from the Pacific Ocean.

When we observe earthshine from the moon in the early evening we see the bright reflection from the Indian Ocean, then as the Earth rotates the continent of Africa blocks this reflection and the moon becomes darker, Langford said. If we find Earth-sized planets and watch their brightness as they rotate, we will be able to assess properties like the existence of land and oceans.

The study appears in the journal Astrobiology.