June 18, 2015

Scientists were thrilled last weekend when the comet lander Philae awoke from a 7-month-long hibernation and contacted scientists on Earth. The lander is part of the Rosetta mission launched by the European Space Agency (ESA) to study comet 67P/Churyumov-Gerasimenko.

An artist’s illustration of Philae on Comet 67P/Churyumov-Gerasimenko. (Credit: DLR German Aerospace Center)

Rosetta is the first space probe to go into orbit around a comet. The ESA launched Rosetta on March 2, 2004, and it arrived at comet 67P in August 2014. Scientists believe that comets preserve dust, ice, and rock from the solar system’s formation. By closely studying the comet, they hope to learn more about the solar system’s makeup and history.

Rosetta carried instruments to study the comet from orbit, but it also carried a small lander named Philae. The lander touched down on the surface of the nucleus on Nov. 12, 2014. Philae was equipped with harpoons that should have anchored it to the comet’s surface. However, the landing failed to trigger the anchors, and the lander rebounded an estimated 0.6 mile (1 kilometer) above the comet’s surface. Philae returned to the comet and bounced one more time before settling in a heavily shaded area. Without sunlight on its solar panels, it could not recharge its batteries. Thus, the lander could only make observations and take readings for about 2 1/2 days before its batteries were depleted.

As 67P moved closer to the sun, more sunlight fell on Philae’s solar panels. The extra light gave the craft enough energy to contact Earth through the Rosetta orbiter on Sunday. The contact was brief, however—only 85 seconds long. ESA scientists are hoping contact can be sustained as the lander receives more energy from the sun.

Other World Book articles:

• Space exploration

• Space exploration (2014-a Back in time article)

December 22, 2014

Earth’s water may not have come from melting comets, according to a paper published in December 2014 by scientists working on the European Space Agency’s Rosetta mission. The Rosetta spacecraft, launched in 2004, went into orbit around P67/Comet Churyumov-Gerasimenko in 2014, landing a small probe on the comet’s nucleus (core) in November.

Most researchers think that the hot, turbulent formation of Earth would have left the early planet dry. Scientist have thus struggled to determine how Earth got its oceans. Most researchers agree that the water was delivered by smaller bodies crashing into the young planet. Such bodies may have been comets or asteroids.

Scientists are still unsure of the source of the water in Earth’s oceans, which cover most of the planet’s surface. This satellite view shows the Indian Ocean, partly bordered by Africa, Asia, and Australia, and below it the Southern Ocean surrounding Antarctica. (NASA/Goddard Space Flight Center and ORBIMAGE/SeaWiFS Project)

Scientists working with an instrument called the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) analyzed water from Comet Churyumov-Gerasimenko to see if it was similar to water found on Earth. Water consists of the elements hydrogen and oxygen. Some of the hydrogen, however, is in a heavier isotope (form) called deuterium. By comparing the ratio of deuterium to ordinary hydrogen in different samples, scientist can tell if the water in each sample is from the same place.

The researchers discovered that the water analyzed by the ROSINA instrument has a higher ratio of deuterium to hydrogen than does Earth’s water. The finding casts doubt that the water on Earth came from comets like Churyumov-Gerasimenko. However, Earth’s water may have come from bombardment by asteroids or from a different population of comets.