Monday, October 19, 2009

Mars Reconnaissance Orbiter - Phoenix against Heimdall crater as it lands

They announced at this morning's press conference that yesterday, when they first looked at their photo of Phoenix under its parachute, the HiRISE team failed to really take in the context of the image. Well, here it is, and -- prepare to have to pick your jaw up off the floor.

Phoenix against Heimdall crater as it lands
This amazing image was captured as Phoenix came in for its Mars landing on May 25, 2008. The HiRISE camera on Mars Reconnaissance Orbiter pointed at Phoenix, which is seen here against the background of a 10-kilometer-diameter crater called Heimdall. The dramatic view makes it appear that Phoenix is falling into the crater, but in fact Phoenix was 20 kilometers closer to HiRISE than Heimdall, and it landed nowhere near the crater. The photo was taken 20 seconds after Phoenix' parachute opened. Credit: NASA / JPL / U. Arizona

Found Here:

MRO's HiRISE camera ac
quired this dramatic oblique image of Phoenix descending on its parachute. Shown here is a a wider view of the full image, showing a 10 kilometer diameter crater informally called �Heimdall,� and an improved full-resolution image of the parachute and lander.

Although it appears that Phoenix is descending into the crater, it is actually about 20 kilometers in front of the crater. It is difficult to believe that it is in front of the crater because it is so much smaller, but in reality it is, and that's a good thing because landing on the steep rocky slopes of the crater would have been far too exciting (or risky).

Images from the lander clearly show t
hat it sits on a flat plain, although the rim of Heimdall may be visible on the horizon. Given the position and pointing angle of MRO, Phoenix is at about 13 km above the surface, just a few seconds after the parachute opened. This improved image shows some details of the parachute, including the gap between upper and lower sections. At the time of this observation, MRO had an orbital altitude of 310 km, traveling at a ground velocity of 3.4 kilometers/second, and a distance of 760 km to the Phoenix lander.

The image was rotated to a position that seems approximately parallel to the horizon based on the elongation of Heimdall crater, but this is not exact. Thus, although Phoenix appears to hang from the parachute at an angle, as if swaying in the wind, the exact geometry has not yet been determined. The parachute image is v
ery sharp as its apparent motion was straight down the HiRISE TDI (time delay integration) columns. However, the surface of Mars was moving at an angle to the TDI columns, and thus is smeared by a few pixels, although the smear is not apparent at the reduced scale of the image shown here.

The sun is almost directly behind HiRISE, so the parachute should be casting a shadow onto the slope of the crater, but we cannot determine which of many dark spots is the shadow until a detailed geometric analysis has been completed.

Found Here:

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