Wonderful new images of Comet 67P/Churyumov-Gerasimenko from Rosetta “ESA’s comet chaser” have been released in the past week or so:

* OSIRIS catches activity in the act –

The comet’s activity has been significantly increasing over the last weeks and months. As the comet moves closer to the Sun along its orbit, its nucleus gets warmer and warmer. Frozen gases sublimate from its surface, carrying dust particles with it and enshrouding the nucleus in a dense coma. With only four months to go until perihelion – the closest point to the Sun – this process is well underway, with pronounced dust jets seen at all times on the comet’s day side.

Rosetta’s OSIRIS wide-angle camera captures the moment a jet bursts
into action. The first image was captured at 07:13 CET on 12 March
2015, the  second two minutes later.
Credits: ESA/Rosetta/MPS for OSIRIS Team 

The two images released today show the remarkable onset of such a jet for the first time. They were taken on 12 March from a distance of 75 kilometres. In the first image, obtained at 07:13 CET, several rays of dust jets frame the upper, illuminated side of the comet. The dark underside shows no such features. Two minutes later, the picture has changed: a spectacular new jet has emerged on the dark side, hurtling dust into space and displaying a clearly discernable fine structure.

“This was a chance discovery,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “No one has ever witnessed the wake-up of a dust jet before. It is impossible to plan such an image.”

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* CometWatch 15 April  –

Today’s CometWatch entry is a single frame NAVCAM image obtained on 15 April, from a distance of 170 km from the centre of Comet 67P/Churyumov-Gerasimenko. At this distance, the resolution is 14.5 m/pixel; the image has been cropped to 11.4 km (the original frame, provided at the end of the post, measures 14.8 km across).

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* CometWatch 15 April – 4 hours later –

Today’s CometWatch entry is another single frame NAVCAM image taken on 15 April, almost four hours after the one that was published last Friday. The new picture was obtained at about 165 km from the centre of Comet 67P/Churyumov-Gerasimenko, where the resolution of NAVCAM is 14 m/pixel. The image has been cropped and measures 10.4 km (the original frame, provided at the end of the post, measures 14.4 km across).

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* “Crescent comet” – CometWatch 15 and 16 April –

The image [below] was captured on 15 April 2015 by Rosetta’s Navigation camera from a distance of 162 km from the comet centre. The resolution is 14 m/pixel and the image measures 14 km across. It has been processed to bring out the incredible detail of the comet’s activity streaming away from the nucleus.

The previous two CometWatch entries were also acquired on 15 April and today’s image fits into the sequence nicely, captured just before midday spacecraft time, a little over two hours after Monday’s entry.

Under the viewing conditions at this time, the comet appears largely in shadow, with the ‘underside’ of the comet’s large lobe beautifully silhouetted against the background glow of activity that surrounds the nucleus.

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* Rosetta update: Two close flybys of an increasingly active comet – The Planetary Society –  Emily Lakdawalla gives a tour of the new images.

In the two months since I last checked up on the Rosetta mission, the comet has heated up, displaying more and more jet activity. Perihelion is now only four months away, and the pictures are just getting more and more dramatic with time.

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The Dawn spacecraft shot past Ceres a month or so and has not been able to see the sunlight side of the dwarf planet until recently as it moves back towards a close orbit around it. It can now see the bright spots that it say on the approach to Ceres:

Ceres’ Bright Spots Come Back Into View

April 20, 2015—The two brightest spots on dwarf planet Ceres, which have fascinated scientists for months, are back in view in the newest images from NASA’s Dawn spacecraft. Dawn took these images on April 14 and 15 from a vantage point 14,000 miles (22,000 kilometers) above Ceres’ north pole.

An animation and still image are available here: www.jpl.nasa.gov/spaceimages/details.php?id=PIA19064

The images show the brightest spot and its companion clearly standing out against their darker surroundings, but their composition and sources are still unknown. Scientists also see other interesting features, including heavy cratering. As Dawn gets closer to Ceres, surface features will continue to emerge at increasingly better resolution.

Dawn has now finished delivering the images that have helped mission planners maneuver the spacecraft to its first science orbit and prepare for subsequent observations. All of the approach operations have executed flawlessly and kept Dawn on course and on schedule. Beginning April 23, Dawn will spend about three weeks in a near-circular orbit around Ceres, taking observations from 8,400 miles (13,500 kilometers) above the surface. On May 9, Dawn will begin to make its way to lower orbits to improve the view and provide higher-resolution observations.

“The approach imaging campaign has completed successfully by giving us a preliminary, tantalizing view of the world Dawn is about to start exploring in detail. It has allowed us to start asking some new and intriguing questions,” said Marc Rayman, Dawn’s mission director and chief engineer, based at NASA’s Jet Propulsion Laboratory, Pasadena, California.

On March 6, Dawn became the first spacecraft to orbit a dwarf planet, and the first to orbit two extraterrestrial targets. Scientists will be comparing Ceres to giant asteroid Vesta, which Dawn studied from 2011 to 2012, in order to gain insights about the formation of our solar system. Both Vesta and Ceres, located in the main asteroid belt between Mars and Jupiter, were on their way to becoming planets before their development was interrupted.

Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK, Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. For a complete list of acknowledgements, visit dawn.jpl.nasa.gov/mission/