Just Passing By

Because the amount of energy necessary for an interplanetary flight is available from practical launch vehicles, spacecraft often use a planet’s gravity to provide some of the energy needed for final trajectories. Properly executed, one or more gravity assist flybys can be enough to change a spacecraft’s speed and direction so it can enter orbit around another world or fly off into the Kuiper Belt or even interstellar space.

This view of Earth was captured in 2007 on the second of three Earth flybys made by ESA’s comet-chasing Rosetta spacecraft on its ten year journey to Comet 67P/Churyumov-Gerasimenko.

Image Credit: ESA

The Changing Face of Comet 67P

A 30-m wide boulder with a mass of almost 13,000 tonnes was found to have moved about 140 m across the face of Comet 67P/Churyumov–Gerasimenko in the months before the comet reached perihelion in August, 2015. That was when the when the comet’s activity was at its highest. In both images above, an arrow points to the boulder; in the right-hand image, the dotted circle outlines the original location of the boulder for reference. The rock was probably moved by jets of material outgassing from the comet.

Image Credit: ESA

A Comet’s Day

This sequence of 23 images of Comet 67P/Churyumov–Gerasimenko was taken with Rosetta‘s OSIRIS narrow-angle camera on 4 July, 2015, about a month before the comet’s closest approach to the Sun. They were taken at 30 minute intervals and span a full “day” at the comet which spins around its axis in roughly 12.4 hours. The images reveal daily color changes on the surface. The bluer areas are richer in water ice than their redder surroundings. A daily cycle of water ice occurs at the comet. Water quickly turns into water vapor when exposed to sunlight during the local daytime, and it condenses back into thin layers of frost and ice as the temperature drops after sunset. Then it sublimate again on the following day. The Sun is toward the top of the frame.

Video Credit: ESA

Philae’s Multiple Landings

Data from both the Philae lander and Rosetta orbiter experiments have been used along with simulations based on Philae’s mechanical design to reconstruct the lander’s attitude and motion during its descent and multiple touchdowns on Comet 67P/Churyumov-Gerasimenko on 12 November, 2014.

[youtube https://www.youtube.com/watch?v=rJ2eqH3Bz4c]

Video Credit: ESA

67P/Churyumov-Gerasimenko at Perihelion

Rosetta_approaching_perihelionThese picture of Comet 67P/Churyumov–Gerasimenko were taken by Rosetta’s OSIRIS narrow-angle camera on 12 August, 2015, just a few hours before the comet reached perihelion, the closest point to the Sun along its 6.5-year orbit,

The image at left was taken at 14:07 GMT, the middle one at 17:35 GMT, and the final image at 23:31 GMT. The spacecraft was about 330 km from the comet. The comet’s activity (at its peak intensity for the next few weeks) is clearly visible; a significant outburst can be seen in the image captured at 17:35.

Image Credit: ESA

Comet Cliffs

cometcliffs_rosetta_960These high cliffs occur on the surface of a comet. They were discovered to be part of the dark nucleus of Comet Churyumov–Gerasimenko by Rosetta, the ESA spacecraft orbiting the comet since early August. These ragged cliffs were imaged by the spacecraft about two weeks ago. Although towering about one kilometer high, the low surface gravity of Comet CG would likely make a jump from the cliffs survivable. At the foot of the cliffs is relatively smooth terrain dotted with boulders as large as 20 meters across.

Image Credit: ESA

A Comet in Color …

ESA_Rosetta_OSIRIS_Color… but not a very much color. Rosetta’s OSIRIS team have produced a color image of Comet 67P/Churyumov-Gerasimenko as it would be seen by the human eye. The comet turns out to be very grey indeed, with only subtle color variations across its surface.

This picture was assembled from three images taken with the Narrow Angle Camera (NAC) of the scientific imaging system OSIRIS in red (744 nm wavelength), green (536 nm), and blue (481 nm) filters on 6 August 2014, from a distance of 120 kilometres. The image area is roughly 4 km square.

Image Credit: ESA

Following the Bouncing Lander

OSIRIS_spots_PhilaeThis mosaic was assembled from a series of images captured by Rosetta’s OSIRIS camera taken over the half-hour spanning the first touchdown of the Philae lander Comet 67P/CG. The time of each of image is marked on the corresponding insets and is in UTC. A comparison of the touchdown area shortly before and after first contact with the surface is shown at the top.

The images were taken with the OSIRIS narrow-angle camera when the spacecraft was 17.5 km from the comet centre, or roughly 15.5 km from the surface. The enlarged insets cover a 17 x 17 m area.

From left to right, the images show Philae descending towards and across the comet before touchdown. The image taken after touchdown, at 15:43 GMT, confirms that the lander was moving east at a speed of about 0.5 m/s as it bounced across the surface of the comet.

Philae‘s actual final landing spot still hasn’t been found. After touching down and bouncing again at 17:25 UTC, it finally landed at 17:32. The mission imaging team believes that by combining the CONSERT ranging data with OSIRIS and navcam images from the orbiter and images from near the surface with data from Philae’s ROLIS and CIVA cameras they will be able to determine the lander’s whereabouts.

Image Credit: ESA

On the Surface of a Comet

Welcome_to_a_cometThe Rosetta mission lander is “safely” on the surface of its comet. One of Philae‘s feet can be seen at the bottom left of this picture of the surface of C67/P Churyumov-Gerasimenko. Philae bounced twice before settling and returning images from the surface, traveling a kilometer or so after ricocheting off of its desired target. A surface panorama suggests that the lander has come to rest tilted and near a shadowing wall. The lander’s solar panels are getting less illumination than if it had landed in the open. The science instruments are working as planned and data is being relayed when the main Rosetta spacecraft is above the lander’s new horizon. However, with good recharging from the solar array, the batteries will not last as long as had been hoped.

Image Credit: ESA