Emily LakdawallaJan 09, 2008

MESSENGER's cameras are working

...but I can't show you any pictures yet.

The MESSENGER mission announced today that the first eight optical navigation images of Mercury have been received on the ground. However, the release didn't actually include the images themselves; I checked with the mission to see if I was just being obtuse in not finding them on the website and was told that no, they aren't actually going to be released until tomorrow's press conference. Now that's just teasing.

So the best I can do is to show you what they should look like, using the handy-dandy Solar System Simulator at JPL; I'm told that the Solar System Simulator now has the most up-to-date information on MESSENGER's trajectory, so the simulations should be accurate. MESSENGER has two cameras, a wide-angle one with a field of view of 10.5 degrees and a narrow-angle one with a field of view of 1.5 degrees, so if you want to see exactly how much Mercury fills the field of view, use the "I want a field of view of __ degrees" option on the Simulator. (10.5 and 1.5 aren't choices you can select from the dropdown, but it's pretty easy to hack the URL to make it show those fields of view.) Here's the wide-angle view as of this moment, and here's the narrow-angle view as of this moment. I should mention that there is a very cool visualization tool for MESSENGER's instruments at the mission website, but the visualization part only covers the closest part of the flyby.

Actually, the Solar System Simulator views are very helpful because it's very clear what part of Mercury was seen by Mariner 10 -- the part that shows craters and stuff in the Simulator views -- and what part has never been seen up close -- the part that is smooth as a billiard ball on Simulator views. As MESSENGER approaches, slightly more than half of the visible hemisphere is what Mariner 10 saw, but if you pay close attention to how much of Mercury is sunlit (just a crescent), you'll see that everything that MESSENGER can see as it comes in for its flyby has already been seen by Mariner 10. It's not until after closest approach that MESSENGER will see terrain not imaged by Mariner 10. And because of the way MESSENGER's communications schedule works out, those images won't start hitting the ground until (probably) January 16, two days after the flyby; and I have no knowledge of how long it will take for the mission to release them to the Internet. Unlike other missions like Cassini, the rovers, and New Horizons, there do not seem to be plans to make a "raw images website" for MESSENGER where images will be made available quickly after their arrival on Earth. So we may have to satisfy ourselves with the visualizations for a while.

I've gathered a bunch of information on the upcoming flyby, including a timeline of science activities. I'll post a longer news story tomorrow after a planned press conference from the mission -- hopefully with some actual images from the spacecraft! -- but in the meantime here is the science activity timeline, for those of you who are on tenterhooks waiting for the first Mercury flyby in 33 years. For a little help in decoding what all the instruments are supposed to do, here's a backgrounder on MESSENGER's instruments.

time (UTC)
Time with
to closest
Jan 14
-30h 00mWide-angle camera approach color movie
With the wide-angle camera, MESSENGER will shoot 86 frames for a movie showing Mercury's crescent growing in the spacecraft's forward view. The movie is being shot purely for public outreach purposes, through the three camera filters necessary to produce it in color; all of the rest of the color imaging during the flyby will employ all 11 of the wide-angle camera's color filters.
Jan 14
-5h 51mMagnetometer to high rate
MESSENGER's magnetometer (MAG) can take measurements of magnetic fields at a variety of rates, from once every 100 seconds to 20 times a second. For the 12 hours surrounding closest approach, it will be operated at its highest rate.
16:14-2h 51mX-ray spectrometer decreases integration times to 60 seconds
As MESSENGER approaches Mercury, the X-ray spectrometer starts taking measurements more rapidly. However, the X-ray spectrometer operates best within about 100 kilometers of Mercury, a distance it won't enjoy until MESSENGER actually goes in to orbit in 2011. Still, data from the 15 minutes surrounding closest approach will be a valuable first look at Mercury with this instrument.
16:24-2h 41mAtmospheric and Surface Composition Spectrometer (MASCS) tail sweeps
Mercury has an extended sodium tail that resembles the tails seen by comets when they are close to the Sun. As it approaches, MESSENGER will roll up and down to carry the MASCS line of sight across the tail, from north to south, in order to map its vertical extent.
17:40-1h 25mWide-angle camera approach color image (5.2 km/pixel)
Mercury will not yet fill the wide-angle camera field of view; 11 images will be taken, through all of the wide-angle camera's filters. Dynamic visualization >
18:03-1h 02mNarrow-angle camera approach mosaic (500 m/pixel)
An 11-by-5 mosaic will cover Mercury's sunlit crescent, all of which is terrain that was imaged by Mariner 10. The narrow-angle camera has no filter wheel, so all of its images are monochrome. Dynamic visualization >
18:04:00-60m 42sGamma-ray spectrometer detectors on at 60s
Similar to the X-ray spectrometer, the gamma-ray spectrometer (GRS) increases the frequency of its observations for the short time around its closest approach to Mercury.
18:19:41-45m 01sLaser altimeter to standby mode
The laser altimeter warms up in preparation for one precious altimetric profile across Mercury, to be taken around closest approach.
18:22:27-42m 15sEarth occultation entry
MESSENGER will pass behind Mercury as seen from Earth; no communications will be received from the spacecraft until it emerges from behind Mercury more than an hour later.
18:52:09-12m 33sTransition to nadir tracking
Now, close to the planet, MESSENGER will rotate so that the laser altimeter can fire downward and measure Mercury's topography.
18:53:00-11m 42sMASCS UV nightside exosphere scans
The MASCS team expects to observe differences in ultraviolet emission from Mercury's dayside and nightside; the dayside emission should be much brighter.
18:54:15-10m 27sEclipse entry
For 13 minutes, MESSENGER will be hidden from the Sun.
19:02:00-02m 42s

MLA to science mode; start firing laser
Dynamic visualization >

19:04:42-00m 00sClosest approach to Mercury
MESSENGER will pass within 200 kilometers of the surface, firing its laser all the time.
19:07:32+02m 50sEclipse exit
19:12:00+07m 18sWide-angle camera: color photometry (0.6-1.25 km/pixel)
Five sets of color images of the same area on Mercury will be snapped as MESSENGER rises quickly from behind Mercury's night side. Because of MESSENGER's motion it will see Mercury's surface illuminated at different angles, until it becomes more than half-full at a phase angle of about 55 degrees. Dynamic visualization 1 >2 >3 >4 >5 >
MASCS ultraviolet, visible, and infrared observations of the dayside surface
With a view of a largely sunlit Mercury, MASCS shifts from observations of the exosphere to measure the composition of the planet's surface.
19:18:00+13m 18sNarrow-angle camera high-resolution mosaic #1 (100-200 m/pixel)
The 4-by-17 mosaic will cover Mercury's equator, in areas unseen by Mariner 10.Dynamic visualization >
MASCS ultraviolet, visible, and infrared dayside exosphere
MESSENGER has now moved farther from Mercury than its eventual elliptical orbit will take it, and MASCS can no longer observe the surface. It will return to observing the exosphere, which should be much brighter than the nightside exosphere.
19:29:00+24m 18sNarrow-angle camera high-resolution mosaic #2 (400-500 m/pixel)
The 9-by-11 mosaic will cover the northern hemisphere, beginning with the pole and moving down to the equatorial area imaged in the previous observation. This and all other departure images mostly cover areas not seen by Mariner 10. (The westermost portion of the Mariner 10-imaged region will be on the sunlit limb.) Dynamic visualization >
19:30:33+25m 51sEarth occultation exit
Although MESSENGER has reappeared from behind Mercury, MESSENGER's radio signals will take almost ten minutes to travel the 170 million kilometers separating it from Earth, so MESSENGER mission control must wait to hear from their spacecraft.
19:31:00+26m 18sLaser altimeter back to standby mode
19:41:00+36m 18sWide-angle camera departure color mosaic (2.5 km/pixel)
A 3-by-3 mosaic of the entire visible globe of Mercury, in 11 colors. Dynamic visualization >
19:56:00+51m 18sNarrow-angle camera departure mosaic #1 (500 m/pixel)
An 11-by-9 mosaic of the entire visible globe of Mercury, at fairly high resolution, will probably be the standout image product of the flyby. The full-resolution image should require nearly 10,000 pixels to go from the north to south poles. Dynamic visualization >
20:04:00+59m 18sGamma-ray spectrometer to longer (300s) measurement interval
20:07+01h 02mNarrow-angle camera departure mosaic #2 (600 m/pixel)
A 10-by-8 mosaic. Dynamic visualization >
20:17+01h 12mWide-angle camera departure color image (4.8 km/pixel)
Mercury will have receded to the point that it fits entirely within the wide-angle camera's field of view. Dynamic visualization >
20:28+01h 23mNarrow-angle camera departure mosaic #3 (750 m/pixel)
An 8-by-6 mosaic. Dynamic visualization >
20:36+01h 31mNarrow-angle camera departure mosaic #4 (800 m/pixel)
A 7-by-6 mosaic. Dynamic visualization >
20:42+01h 37mNarrow-angle camera departure movie (1.6 to 22 km/pixel)
At the start of this movie, Mercury will fill the narrow-angle camera field of view. A total of 288 frawmes will be shot over the next 18.5 hours at a rate of one frame every five minutes. In the final image taken during the encounter, Mercury will still be more than 200 pixels across.
22:14+03h 9mX-ray spectrometer returns to long integration time (300s)
January 15
+05h 59mNeutron spectrometer returns to low-rate mode
Fast Imaging Plasma Spextrometer returns to low-rate mode
01:14+06h 09mMagnetometer returns to low-rate mode
19:04+23h 59mEnergetic Particle and Plasma Spectrometer returns to low-rate mode
19:14+24h 09mX-ray spectrometer surface sensors off, solar sensor remains on
January 16 Gamma-ray spectrometer returns to cruise configuration
Radio science data collection ends

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