MESSENGER’s Farewell Venus Video


NASA’s MESSENGER spacecraft made its second and final flyby with the planet Venus on June 5th, 2007. It captured images and data on the way in, and it did the same as it sped away from the cloudy inner planet. The imaging team working with Messenger have stitched together the outbound images into a video, 50 frames long.

The images were captured using MESSENGER’s Wide Angle Camera. At the beginning of the sequence, the spacecraft was only 60,688 kilometers (37,710 miles) away from Venus, and at the end, it was 89,310 kilometers (55,495 miles) away. The first set of images were taken every 20 minutes, and then every 60 minutes at the end.

Click here to watch the video. Warning, it’s a 3 MB download, so this is only for the bandwidth unimpaired.

This is the end of MESSENGER’s visits to Venus, but that just means it’s time to get ready for the big show: Mercury. In January 2008, the spacecraft will make its first flyby of Mercury, and then two more on October 6th, 2008 and September 29th, 2009. It will make its final insertion maneuver on March 18, 2011.

Once it’s in a final mapping orbit, MESSENGER will begin analyzing Mercury with a suite of scientific instruments. These are designed to answer several key questions:

Why is Mercury so dense? Of all the inner planets, it’s the most dense by far. In fact, according to calculations, it would have to be 65% metal, twice as much as the Earth. One theory proposes that the planet became enriched with metal during its formation in the early solar nebula. Another possibility is that radiation from the Sun blasted away the outer rock layer of Mercury, leaving the iron rich core.

What is its geologic history? Only 45% of Mercury has ever been photographed by spacecraft. The part that was seen is heavily cratered and ancient, like the Earth’s moon. But there are younger plains between some of the older craters, and scientists think these could indicate volcanism in the planet’s history.

What is the structure of Mercury’s core? Scientists were surprised to discover that Mercury has a global magnetic field. This is a characteristic that it shares with the Earth. We know that the Earth has a liquid metal core, that acts as a natural dynamo. Does Mercury have one too?

What is the nature of Mercury’s magnetic field? Scientists are just beginning to understand the interactions between the Earth’s magnetic field, and the Sun’s solar wind. How does Mercury’s magnetic field differ from our own?

What are the unusual materials at Mercury’s poles? Mercury’s rotation is oriented so that its axis of rotation is nearly perpendicular to its angle of orbit. This means that in the polar regions, the sunlight hits the surface at a constant grazing angle. The interiors of some craters are in permanent shadow, and could have tiny deposits of water ice.

What’s the story with its atmosphere? You might be surprised to know, but Mercury has a thin atmosphere. It’s so thin that the gas particles don’t collide with each other. Instead, they bounce across Mercury’s surface; the official name for this is an exosphere.

So many questions. I can’t wait for MESSENGER to get to Mercury.

Original Source: MESSENGER News Release

Flyby Images of Venus from MESSENGER


NASA’s MESSENGER spacecraft made its second flyby of Venus earlier in June, and scientists have now released the images. The photographs attached to this story actually show the pictures the spacecraft captured as it was traveling away from Venus, on its way to an encounter with Mercury in the future.

MESSENGER has a suite of instruments designed to map out the details of Mercury’s surface; unfortunately, Venus is obscured by thick clouds, so it wasn’t able to see down to map out the terrain and minerals. That task will have to wait until it reaches Mercury. However, it did get an opportunity to observe the cloudy planet at the same time ESA’s Venus Express was observing. Scientists will be able to compare images, combine data, and calibrate scientific instruments from this double view.

The spacecraft has now past Venus for the last time; all of its future planetary encounters will be with Mercury. It will make three flybys of the closest planet to the Sun before going into orbit in 2011.

Original Source: NASA/JPL/JHUAPL News Release

Mercury is Soft in the Middle


A team of astronomers has discovered that tiny Mercury has a molten core, just like our own planet. The discovery was made using three ground-based radio observatories that bounced radio waves off the planet, and then analyzed the return signals.

Before this research, scientists were divided about the structure of Mercury. Most models predicted that it has an iron-rich core, but it wasn’t known if it had completely cooled, or was still liquid inside. Trace quantities of sulfur and other chemicals could have mixed in with the planet while it was forming, and this kept it from completely solidifying over time.

The astronomers first beamed a series of radio waves at the surface of Mercury, and then measured them as they bounced off the surface and returned to Earth. The returned signals were analyzed by a trio of radio telescopes: the Arecibo Observatory in Puerto Rico, NSF’s Robert C. Byrd Green Bank Telescope, and the NASA/JPL 70-meter antenna at Goldstone, California.

They were able to detect a wobbling of the signal that was double what you would expect from a planet with a solid core, but exactly the right amount for a planet with a liquid core.

Their research is the cover story of the May 4, 2007 edition of the Journal Science.

Original Source: NSF News Release

Mercury’s Transit Captured by Hinode

The Japanese solar observing spacecraft Hinode captured this photograph of Mercury’s transit this week. Hinode, formerly known as Solar B, is currently in its shakedown period, where controllers ensure that each of its scientific instruments are working. But they couldn’t pass up this opportunity, so they pointed the spacecraft at the Sun, and watched the entire transit. Hinode should resume its normal science operations next month.
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MESSENGER Flips Over to Get Some Shade

As NASA’s MESSENGER spacecraft gets closer to Mercury, it’s also flying closer to the Sun. And temperatures are rising. The spacecraft rotated 180-degrees on June 21, pointing its sunshade towards the Sun. This will keep temperatures to safe levels within the spacecraft. MESSENGER will keep this shade between itself and the Sun for the remainder of its mission. The spacecraft’s next big event will be its flyby with Venus on October 24.
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