MESSENGER is NASA’s mission to the planet Mercury, and this coming Monday it will make its first pass at the planet.
Getting to Mercury is tough; it orbits the Sun a whole lot faster than the Earth does, so we need to play some pretty serious orbital mechanical billiards to get a probe there and insert it into orbit. MESSENGER already flew past Venus recently, and will make several flybys of Mercury before settling into orbit in 2011.
I’m sure we’ll be seeing pictures of the tiny hot planet coming from the mission very soon, early next week. Keep your eyes here; I’ll get them as soon as I can. Also keep Emily Lakdawalla’s blog on your bookmark list, since she seems supernaturally able to get pictures on her blog I’ve never seen before.
January 10th, 2008 at 4:26 pm
How close to the SUN does Messenger get? And what kind of shielding is required to keep the probe safe?
January 10th, 2008 at 5:52 pm
MESSENGER is meant to drop into orbit around Mercury. So it gets fully as close to the Sun as Mercury itself.
As for the flyby, Celestia shows Mercury positioned such that slightly less than half of the day side is on the part that Mariner 10 didn’t get to see. There’s 55 percent of that planet for which we have no photos.
January 10th, 2008 at 6:01 pm
Sorry, I typed my question in a bit of a rush; what I meant was how close does it get to the Sun during the actual flyby? Does it sweep way inside Mercury’s orbit or just barely inside (if at all)?
(It would be great if Messenger had a cup it could dip down into the Sun ala the Ray Bradbury story…;) )
January 10th, 2008 at 6:27 pm
This is fantastic. It’s amazing to think that we can take such a relatively small object and use gravity slingshots and such to put it into orbit around another planet. Getting to Pluto is mind-boggling due to the distances involved, but really, getting Messenger to be a satellite of Mercury is just as great a feat. At perihelion, its orbital speed is almost twice that of Earth.
Also, I was kind of sad to see that the odds of the impact of 2007 WD5 with Mars are slim to none: 1 in 10,000.
http://neo.jpl.nasa.gov/news/news156.html
January 10th, 2008 at 6:34 pm
The mighty Wikipedia has a diagram (I don’t know where I’d find it on a NASA site) and it looks like the flyby is just outside Mercury’s orbit. So MESSENGER passes on the night side, and not inside the orbit at any point. Still that’s closer to the Sun than Mariner 10 ever went: it met Mercury at its aphelion, and was itself settled into a heliocentric orbit with twice the period of Mercury, while MESSENGER appears to be meeting Mercury closer to perihelion. Mercury’s orbit is rather eccentric.
If it passes on the night side, we won’t get to see all of the day side. We’ll see a fat crescent coming in and a fat crescent going away, with a gap between them — illuminated, but the view is blocked. But one of those views should be on the part that Mariner 10 never saw.
As for shielding, the basic idea is you put a big reflector on one side and keep that facing the sun. It simply reflects most of the radiation, and the shaded side faces into space and keeps the electronics cool.
January 10th, 2008 at 7:13 pm
MandyDax says: “Getting to Pluto is mind-boggling due to the distances involved, but really, getting Messenger to be a satellite of Mercury is just as great a feat. At perihelion, its orbital speed is almost twice that of Earth.”
I agree to both of those, but from an energy standpoint it’s easier to get to Pluto than to Mercury. The Earth is more than halfway out of the Sun’s gravity well, so to get to Pluto you have to add less energy than you have to take away to get to Mercury.
And while Mercury’s tangential speed may be greater than the Earth’s, its angular momentum is less (which is what determines your orbit in a non-relativistic universe).
- Jack
January 10th, 2008 at 9:59 pm
This is quite exciting. A bit of Mercury trivia, Caloris basin is named from the latin for Heat (same root as calorie) and it was so named because it gets the brunt of Mercury’s infamous double sunrise. Another open question is if the poles will get any attention. There is the signature for ice at the poles making them a good place for a human mission.
January 11th, 2008 at 12:22 am
I am really looking forward to whatever MESSENGER finds during its mission. We are just beginning to seriously poke around our planetary system; the little we’ve found so far is astounding.
Hot volcanoes on Io; possibly COLD volcanoes on Titan, what could be an enormous lava cave on Mars… and possibly ice on the innermost planet itself. This is a great time to be alive, to see this exploration unfold.
January 11th, 2008 at 3:36 am
I’ve been on the edge of my seat since yesterday. I love all this exploration stuff it blows me away.
The first image is online already; it’s a shot taken to confirm Messenger’s position for the first approach. Modest image, but it’s now my wallpaper.
http://messenger.jhuapl.edu/gallery/sciencePhotos/
The team has a great website.
http://messenger.jhuapl.edu/
Louise Prockter is my hero.
Bob(Big)
January 11th, 2008 at 4:58 am
Now here’s the #2 thing I waited for a long time! A return to Mercury! (#1 is a stop to Pluto. And I’ll still have long to wait. Sniffle.)
I can’t wait to see the pictures. It will be awesome. Are they taking any right now or just waiting for the target flyby day?
January 11th, 2008 at 8:37 am
According to Louise Prockter:
“Thirty hours before the closest approach point, we begin taking a 3 color movie of Mercury, which continues until about 2 hours before closest approach. We will be looking a crescent Mercury, and we will image some of the terrain that was observed by Mariner 10 back in the 1970’s. We then take a monochrome mosaic and an 11-filter color image of the same part of the surface.
During the closest part of the flyby, we are in shadow, so won’t be taking any images for about an hour. As we approach the terminator, we use the MDIS pivot to look ahead along the spacecraft ground track, and image a region that is in the sunlight part. Once we cross the terminator, we image this area another four times as we fly over it, in order to gather information about the texture of the surface as the viewing geometry changes. We also take our highest-resolution images of the surface at this time – from 100-200 m/pixel.
We are now taking images of the hemisphere of Mercury that has never before been seen by a spacecraft.
As we fly away from Mercury, we take a number of monochrome and color images of the same area, at a variety of resolutions down to ~1 km/pixel in monochrome, and ~5 km/pixel in color. Finally, about 2 hours after the closest approach point, we begin taking a monochrome departure movie, where we take 1 image every 5 minutes for another 18 hours.These images will be compared to the “known” hemisphere of Mercury, but they will be at generally higher resolution than Mariner 10, and some of them are in 11 filters instead of the 3 that Mariner 10 acquired.”
January 11th, 2008 at 8:58 am
There’s a new image out
http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=109
Bring it on
January 11th, 2008 at 10:58 am
One question here……. In Emily’s blog, she says that “The primary goal of the first Mercury encounter is to slow the spacecraft by 5,000 miles per hour”. Yet on the MESSENGER website, the speed of the spacecraft relative to the Sun increases from 40.6 km/s to 41.9 km/s as a result of the flyby. What am I missing here?
January 11th, 2008 at 10:59 am
Troy: “Another open question is if the poles will get any attention.”
My recollection is that MESSENGER will be a polar orbiter, so yes, the poles will feel the love.
Also: there’s a heat-shield on the spacecraft to keep the sunlight off of it. The unshielded side will still bake quite a bit when it’s facing Mercury’s day-side, however.
January 11th, 2008 at 12:58 pm
John writes:
[[Also: there’s a heat-shield on the spacecraft to keep the sunlight off of it. The unshielded side will still bake quite a bit when it’s facing Mercury’s day-side, however.]]
Good point! Thermal emission, and reflected sunlight, from a planet has to be taken into account in planning around a satellite’s environment. Mercury’s bolometric Bond albedo isn’t very high — I think 0.119 was what Bonnie Buratti’s team found in the ’90s — but the thermal radiation will pouring off that baby. Hang on, I feel compelled to do the math.
Solar constant at Mercury, assuming it’s exactly at the 0.387 AU midpoint of its orbit: 9,121.4 watts per square meter (I assume S at Earth’s orbit is 1,366.1 W m-2, which is the mean for Judith Lean’s data for 1951-2000). Mercury reflects back 1,085.4 W m-2 at shortwave wavelengths.
Subsolar temperature given the known semimajor axis and albedo: 558.0 K. Given perfect emissivity (e = 1.0), the thermal radiation given off should then be 5,497.3 W m-2 (I’ve got too many significant digits there, of course). So about five times as much thermal IR as shortwave. Thank God for the inverse square law. Presumably this baby won’t get closer than 100 km or so…?
January 11th, 2008 at 1:00 pm
Okay, the first “baby” there referred to Mercury and the second to the Messenger probe. Sorry about the confusion.
January 11th, 2008 at 4:21 pm
[...] Bad Astronomy Blog » MESSENGER makes a pass at Mercury Monday MESSENGER is NASA’s mission to the planet Mercury, and this coming Monday it will make its first pass at the planet. W00t!!!! CANNOt wait t see the images coming down next week:) (tags: astronomy messenger mercury nasa) [...]