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It’s Raining on Saturn

By David Reneke

David Reneke’s wrap-up of space and astronomy news.

It seems crazy to talk about rain on Saturn, but it turns out to be true. Saturn’s rings give off a form of rain that falls onto the planet below, covering larger areas than previously thought.

Based on NASA-funded observations and analysis led by the University of Leicester, a new study has found that the rain affects the make-up and temperature structure of parts of Saturn’s upper atmosphere. “Saturn is the first planet to show significant interaction between its atmosphere and ring system,” said James O’Donoghue, a postgraduate researcher at Leicester and lead author of a paper in Nature.

In effect, the rain’s main effect is to reduce the number of electrons in a given space in Saturn’s upper atmosphere. This explains why those electron levels are unusually low at some latitudes. The work also helps us understand the development of the ring system and changes in Saturn’s atmosphere.

“It turns out that a major driver of Saturn’s ionospheric environment and climate across vast reaches of the planet are ring particles located some 60,000 kilometres overhead,” explained Kevin Baines of NASA’s Jet Propulsion Laboratory. “The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool.”

In the early 1980s, images from NASA’s Voyager spacecraft showed several dark bands on Saturn. Scientists assumed water could have been showering down into those bands from the rings. The indistinct bands weren’t seen again until the team conducting the new work looked at Saturn in near infrared light.

In Saturn’s ionosphere, charged particles are produced when the normally neutral atmosphere is exposed to a flow of energetic particles from the Sun. When the scientists tracked the pattern of emissions they expected to see a uniform glow of infrared light across the planet. Instead, a series of light and dark bands appeared, with the dark areas corresponding to water-rich parts of Saturn’s rings and light bands corresponding to gaps in the rings.

The scientists surmised that charged water particles from the planet’s rings were being drawn towards the planet along Saturn’s magnetic field lines, neutralising the emissions and leaving a shadow over 30–43% of the planet’s upper atmosphere surface.

Both Earth and Jupiter have uniformly glowing equatorial regions. Scientists expected the same at Saturn, but they instead saw dramatic differences at different latitudes.

Further observations using instruments onboard the Cassini spacecraft may reveal more detail about the way that water is removing charged particles and effects at different times of the day.

Kepler Finds 461 New Planet Candidates

NASA’s Kepler mission has produced an embarrassment of riches with the team announcing the discovery of 461 new planet candidates. Four of the potential new planets are less than twice the size of Earth and orbit in their sun’s “habitable zone”, the region in the planetary system where liquid water might exist on the surface of a planet.

One of the four newly identified super Earth-sized planet candidates, KOI-172.02, orbits in the habitable zone of a star similar to our sun. The possible planet is approximately 1.5 times the radius of Earth and orbits its host star every 242 days.

Based on recent observations, Kepler’s findings show a steady increase in the number of smaller planet candidates and the number of stars with more than one candidate. “There is no better way to kick off the start of the Kepler extended mission than to discover more possible outposts on the frontier of potentially life bearing worlds,” said Christopher Burke, Kepler scientist at the SETI Institute in California, who is leading the analysis.

Since Kepler’s last catalogue released in February 2012, the number of candidates discovered in the Kepler data has increased by 20% and now totals 2740 potential planets orbiting 2036 stars. Interestingly, 43% of Kepler’s planet candidates have neighbouring planets – a big plus for finding ET.

The Kepler space telescope identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars in search of planets that pass in front of their host star. At least three transits are required to verify a potential planet.

To identify the potential new planets the scientists analysed more than 13,000 transit-like signals to eliminate known spacecraft instrumentation and astrophysical false positives, phenomena that masquerade as planetary candidates.

Candidates require additional follow-up observations and analyses to be confirmed as planets. At the beginning of 2012, 33 candidates in the Kepler data had been confirmed as planets. Today there are 105.

“The analysis of increasingly longer time periods of Kepler data uncovers smaller planets in longer period orbits – orbital periods similar to Earth’s,” said Steve Howell, Kepler mission project scientist at Ames. “It is no longer a question of will we find a true Earth analogue, but a question of when.”

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com