Cassini Flyby of Enceladus

The spacecraft Cassini did a flyby of Saturn's moon Enceladus five days ago, on March 12th. This flyby was unique in that Cassini flew by Enceladus at the height of a mere 50 kilometers (31 miles) above the surface of the moon. This particular video was made by Brent Buffington, who's a Cassini navigation team member. The animation shows Cassini preparing for the flyby and then shooting past the moon. As Cassini swings past Enceladus, the spacecraft rotates into various positions, allowing each instrument on board to take measurements. The left-hand window shows the field-of-view for the prime instrument, while the right-hand windows show the view from the different instrument boresights. The instruments include:

UVIS (Ultraviolet Imaging Spectrograph) - a long narrow magenta field of view

VIMS (Visible-Infrared Mapping Spectrometer) - a big red square

ISS (Imaging Subsystem; i.e., the visible light camera) - a white square; a small white square is the narrow angle camera, a large white square is the wide angle camera

CIRS (Composite Infrared Spectrometer) - a red circular field-of-view and two small red parallel narrow fields-of-views

HGA (High Gain Antenna; used for communicating with Earth)

Radar - a green circle, centered on the high gain antenna

The video can also be viewed at Youtube.

Credit: NASA

WMAP Reveals Neutrinos, End of Dark Ages, First Second of Universe

Credit (all illustrations): NASA/WMAP Science Team

NASA released this week five years of data collected by the Wilkinson Microwave Anisotropy Probe (WMAP) that refines our understanding of the universe and its development. It is a treasure trove of information, including at least three major findings:

New evidence that a sea of cosmic neutrinos permeates the universe

Clear evidence the first stars took more than a half-billion years to create a cosmic fog

Tight new constraints on the burst of expansion in the universe's first trillionth of a second

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WMAP measures a remnant of the early universe - its oldest light. The conditions of the early times are imprinted on this light. It is the result of what happened earlier, and a backlight for the later development of the universe. This light lost energy as the universe expanded over 13.7 billion years, so WMAP now sees the light as microwaves. By making accurate measurements of microwave patterns, WMAP has answered many longstanding questions about the universe's age, composition and development.

The universe is awash in a sea of cosmic neutrinos. These almost weightless sub-atomic particles zip around at nearly the speed of light. Millions of cosmic neutrinos pass through you every second.

"A block of lead the size of our entire solar system wouldn’t even come close to stopping a cosmic neutrino,” said science team member Eiichiro Komatsu of the University of Texas at Austin.

WMAP has found evidence for this so-called "cosmic neutrino background" from the early universe. Neutrinos made up a much larger part of the early universe than they do today.

Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos.

Cosmic neutrinos existed in such huge numbers they affected the universe’s early development. That, in turn, influenced the microwaves that WMAP observes. WMAP data suggest, with greater than 99.5% confidence, the existence of the cosmic neutrino background - the first time this evidence has been gleaned from the cosmic microwaves.

Much of what WMAP reveals about the universe is because of the patterns in its sky maps. The patterns arise from sound waves in the early universe. As with the sound from a plucked guitar string, there is a primary note and a series of harmonics, or overtones. The third overtone, now clearly captured by WMAP, helps to provide the evidence for the neutrinos.

The hot and dense young universe was a nuclear reactor that produced helium. Theories based on the amount of helium seen today predict a sea of neutrinos should have been present when helium was made. The new WMAP data agree with that prediction, along with precise measurements of neutrino properties made by Earth-bound particle colliders.

Another breakthrough derived from WMAP data is clear evidence the first stars took more than a half-billion years to create a cosmic fog. The data provide crucial new insights into the end of the "dark ages," when the first generation of stars began to shine. The glow from these stars created a thin fog of electrons in the surrounding gas that scatters microwaves, in much the same way fog scatters the beams from a car’s headlights.

"We now have evidence that the creation of this fog was a drawn-out process, starting when the universe was about 400 million years old and lasting for half a billion years," said WMAP team member Joanna Dunkley of the University of Oxford in the U.K. and Princeton University in Princeton, N.J. "These measurements are currently possible only with WMAP."

A third major finding arising from the new WMAP data places tight constraints on the astonishing burst of growth in the first trillionth of a second of the universe, called “inflation,” when ripples in the very fabric of space may have been created. Some versions of the inflation theory now are eliminated. Others have picked up new support.

"The new WMAP data rule out many mainstream ideas that seek to describe the growth burst in the early universe," said WMAP principal investigator, Charles Bennett, of The Johns Hopkins University in Baltimore, Md. "It is astonishing that bold predictions of events in the first moments of the universe now can be confronted with solid measurements."

The five-year WMAP data were released this week, and results were issued in a set of seven scientific papers submitted to the Astrophysical Journal.

Prior to the release of the new five-year data, WMAP already had made a pair of landmark finds. In 2003, the probe's determination that there is a large percentage of dark energy in the universe erased remaining doubts about dark energy's very existence. That same year, WMAP also pinpointed the 13.7 billion year age of the universe.

The Earth and Moon from Mars

Credit: NASA/JPL-Caltech/University of Arizona

This is an image of Earth and the moon, acquired on October 3, 2007, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

At the time the image was taken, Earth was 142 million kilometers (88 million miles) from Mars, giving the HiRISE image a scale of 142 kilometers (88 miles) per pixel, an Earth diameter of about 90 pixels and a moon diameter of 24 pixels. The phase angle is 98 degrees, which means that less than half of the disk of the Earth and the disk of the moon have direct illumination.

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On the day this image was taken, the Japanese Kayuga (Selene) spacecraft was en route from the Earth to the moon, and has since returned spectacular images and movies.

On the Earth image we can make out the west coast outline of South America at lower right, although the clouds are the dominant features. These clouds are so bright, compared with the moon, that they are saturated in the HiRISE images. In fact the red-filter image was almost completely saturated, the blue-green image had significant saturation, and the brightest clouds were saturated in the infrared image. This color image required a fair amount of processing to make a nice-looking release. The moon image is unsaturated but brightened relative to Earth for this composite. The lunar images are useful for calibration of the camera.

NASA: New Radar Maps of the Moon's South Pole

Above: This movie is a simulation of the amount of solar illumination in the south polar region of moon over a solar day generated using high resolution topography. (Credit: NASA)

NASA has obtained new high-resolution radar maps of the Moon's south pole--a region the space agency is considering as a landing site when astronauts return to the Moon in the years ahead.

"We now know the south pole has peaks as high as Mt. McKinley and crater floors four times deeper than the Grand Canyon," says Doug Cooke, deputy associate administrator for the Exploration Systems Mission Directorate at NASA Headquarters. "These data will be an invaluable tool for advance planning of lunar missions."

Scientists at NASA's Jet Propulsion Laboratory collected the data using the Goldstone Solar System Radar located in California's Mojave Desert. Three times in 2006, JPL scientists targeted the moon's south polar region using Goldstone's 70-meter radar dish. The antenna, three-quarters the size of a football field, sent a 500-kilowatt strong, 90-minute long radar stream 231,800 miles to the Moon. The radar illuminated the rough-hewn lunar surface over an area measuring about 400 by 250 miles. Signals were reflected back to two of Goldstone's 34-meter antennas on Earth. Scientists have been analyzing the echoes ever since, and the data were released by NASA for the first time this week.

NASA is eying the Moon's south polar region as a possible site for future outposts. The location has many advantages; for one thing, there is evidence of water frozen in deep dark south polar craters. Water can be split into oxygen to breathe and hydrogen to burn as rocket fuel--or astronauts could simply drink it. Planners are also looking for "peaks of eternal light." Tall polar mountains where the sun never sets might be a good place for a solar power station.

These are the highest-resolution maps to date. The best images, previously, were generated by the Clementine spacecraft, which could resolve lunar terrain features near the south pole at 1 kilometer per pixel. The JPL radar maps are 50 times more detailed.

As wonderful as they are, however, these images will pale in comparison to next-generation photos from NASA's Lunar Reconnaissance Orbiter. The spacecraft is scheduled to launch in late 2008 and its camera will beam back photos of the moon with details as small as 1 meter.

The International Space Station by Atlantis (STS-122)

Credit: ESA/NASA

Backdropped by the blackness of space, the International Space Station is seen from Space Shuttle Atlantis as the two spacecraft begin their relative separation. Earlier the STS-122 and Expedition 16 crews concluded almost nine days of cooperative work onboard the shuttle and station. Undocking of the two spacecraft occurred at 3:24 a.m. (CST) on Feb. 18, 2008.

Columbus Laboratory, by STS-122

Credit: NASA

As of the time of this writing, STS-122, on board the Space Shuttle Atlantis, is five and one-half days into a planned 12-day mission. The primary objective for STS-122 is to install the ESA's Columbus Laboratory on to the International Space Station, which, the Minister, is happy to report, has been a success so far to date. One of the other objectives for this flight is that Flight Engineer Daniel M. Tani of Expedition 16 will be returning home to Earth, with his place being taken by Léopold Eyharts, of France. Atlantis is currently scheduled to return to Earth next Tuesday, February 19th.

In the above image, the Columbus Laboratory sits in Atlantis' payload bay (the large grey object with the "ESA" sign). Also visible are the vertical stabilizer, the orbital maneuvering system (OMS) pods and, of course, the Earth. This photo was taken on February 8th, the second day of the flight, by an STS-122 crewmember.

The Sun, by SOHO

Credit: SOHO (ESA & NASA)

A number of spacecraft observe our Sun. One mission, which has been in operation for almost a dozen years now, is the Solar & Heliospheric Observatory (SOHO). Launched on December 2, 1995 and beginning operations in May 1996, SOHO is a joint collaboration between the European Space Agency and NASA to study the Sun from the core to the outer corona and the solar wind. SOHO is also the primary provider for near-real time data of the Sun's activities, which allows astronomers to forecast space weather.

One of the instruments aboard SOHO is the Extreme Ultraviolet Imaging Telescope or EIT. The EIT studies the lower corona and the transition region between the chromosphere and the corona by taking full disc images of the Sun at four selected wavelengths in the extreme ultraviolet. These wavelengths correspond to temperatures between 80,000 and 2,500,000°C.

The above image is a composite of three separate images, taken in May 1998, at 171Å (Angstrom; the blue image), 195Å (green) and 284Å (yellow). Each wavelength reveals solar features unique to that wavelength. Since the EIT images come from the spacecraft in black and white, they are color coded for easy identification.

Neptune, by Voyager 2

Credit: NASA


While Neptune may be the farthest of the eight planets orbiting the Sun (as defined by the International Astronomical Union (IAU)), it certainly doesn't lack for interesting features. While Uranus' atmosphere is primarily a mix of hydrogen, helium and methane (the last giving the planet its light blue hue), Neptune's atmosphere is primarily made up of methane, which is what gives the planet its deep blue color. Neptune is the smallest of the four gas giants, but it's also the densest of that set.

Although Neptune receives only 3% as much sunlight as Jupiter, it showed several large dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot is named the "Great Dark Spot" and is an anticyclone similar to Jupiter's Great Red Spot. Neptune's Great Dark Spot is comparable in size, relative to the planet, and at the same latitude (22° South latitude) as Jupiter's Great Red Spot. However, Neptune's Great Dark Spot is far more variable in size and shape than the Great Red Spot. Another spot, named "D2" by the Voyager 2 scientists, is located far to the south of the Great Dark Spot, at 55° South latitude. It is almond-shaped, with a bright central core, and moves eastward around the planet in about 16 hours.

Most of the winds on Neptune blow in a westward direction, which is retrograde, or opposite to the rotation of the planet. Near the Great Dark Spot, there are retrograde winds blowing up to 1,500 miles an hour (2,400 kph) -- the strongest winds measured on any planet, including windy Saturn.

The only spacecraft to date to fly past Neptune was Voyager 2, which hurtled past Neptune's north pole on August 25, 1989. Voyager 2's closest approach was a mere 4,950 km from the planet, the closest approach Voyager 2 made of any planet. The fly-by of Neptune put Voyager 2 on a course 48° south of the ecliptic plane of the solar system, roughly toward the constellation Canis Major and the star Sirius, with a rate of speed about 470 million km per year.

Uranus, by Voyager 2

Credit: NASA

The fly-by of Voyager 2 past the planet Uranus should have been one of excitement and wonder as it had been in July 1979 and August/September 1981, when Voyager passed by the planets Jupiter and Saturn, respectively. However, four days after Voyager's closest approach to Uranus, the Space Shuttle Challenger was destroyed and the new discoveries from the outer solar system were quickly ignored in the wake of the tragedy.

This photo was taken by Voyager 2 on January 25, 1986, the day after the closest approach, at a distance of 600,000 miles (about 965,000 km). Voyager 2 is still operational, over 40 years after its launch, and is over 85.039 Astronomical Units (AU) or 7.9 billion miles (12.7 billion km) away from the Sun at this time.

Saturn, by Cassini

Credit: NASA/JPL/Space Science Institute

This natural color mosaic was acquired by the Cassini spacecraft as it soared 39 degrees above the unilluminated side of Saturn's rings.

Little light makes its way through the rings to be scattered in Cassini's direction in this viewing geometry, making the rings appear somewhat dark compared to the reflective planet. The view can be contrasted with earlier mosaics designed to showcase the rings rather than the planet, which were therefore given longer exposure times (see Blinding Saturn and Ring World).

Bright clouds play in the blue-gray skies of the north. The ring shadows continue to caress the planet as they slide farther south toward their momentary disappearance during equinox in 2009. The rings' reflected light illuminates the southern hemisphere on Saturn's night side.

The scene is reminiscent of the parting glance of NASA's Voyager 1 as it said goodbye to Saturn in 1981 (see PIA00335). Cassini, however, will continue to orbit Saturn for many years to come.

Three of Saturn's moons are visible in this image: Mimas (397 kilometers, or 247 miles across) at the 2 o'clock position, Janus (181 kilometers, or 113 miles across) at the 4 o'clock position and Pandora (84 kilometers, or 52 miles across) at the 8 o'clock position. Pandora is a faint speck just outside the narrow F ring.

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The view combines 45 images -- 15 separate sets of red, green and blue images -- taken over the course of about two hours, as Cassini scanned across the entire main ring system.

The images in this view were obtained on May 9, 2007, at a distance of approximately 1.1 million kilometers (700,000 miles) from Saturn. Image scale is about 62 kilometers (39 miles) per pixel.

Jupiter and Io, by New Horizons

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

This is a montage of New Horizons images of Jupiter and its volcanic moon Io, taken during the spacecraft’s Jupiter flyby [pdf] in early 2007. The Jupiter image is an infrared color composite taken by the spacecraft’s near-infrared imaging spectrometer, the Linear Etalon Imaging Spectral Array (LEISA) at 1:40 UT on Feb. 28, 2007. The infrared wavelengths used (red: 1.59 µm, green: 1.94 µm, blue: 1.85 µm) highlight variations in the altitude of the Jovian cloud tops, with blue denoting high-altitude clouds and hazes, and red indicating deeper clouds. The prominent bluish-white oval is the Great Red Spot. The observation was made at a solar phase angle of 75 degrees but has been projected onto a crescent to remove distortion caused by Jupiter’s rotation during the scan. The Io image, taken at 00:25 UT on March 1st 2007, is an approximately true-color composite taken by the panchromatic Long-Range Reconnaissance Imager (LORRI), with color information provided by the 0.5 µm (“blue”) and 0.9 µm (“methane”) channels of the Multispectral Visible Imaging Camera (MVIC). The image shows a major eruption in progress on Io’s night side, at the northern volcano Tvashtar. Incandescent lava glows red beneath a 330-kilometer high volcanic plume, whose uppermost portions are illuminated by sunlight. The plume appears blue due to scattering of light by small particles in the plume.

Butterfly Crater in Hesperia Planum, by Mars Express

Credits: ESA/DLR/FU Berlin (G. Neukum)

The Ministry of Space Exploration has a sister blog, Areology, that focuses on the exploration of Mars. As a result, the Ministry will not discuss that planet here as much as the others. Please visit Areology.

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows a large elliptical impact crater in the Hesperia Planum region of Mars.

The HRSC obtained these images during orbit 368 with a ground resolution of approximately 16.7 meters per pixel. The scenes show the region of Hesperia Planum, at approximately 35.3° South and 118.7° East.

[The crater measures] ...approximately 24.4 km long, 11.2 km wide and reaching a maximum depth of approximately 650 meters below the surrounding plains.

Ejecta from this impact can be seen extending away from the crater, including two prominent lobes of material north-west and south-east of the crater.

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This appears to be an impact crater that was subsequently resurfaced by lava flows, preserving the outline of the underlying crater. The curving features visible in the north of the image, known as 'wrinkle ridges,' are caused by compressional tectonics.

While the majority of impact craters are relatively circular, the elliptical shape of this impact crater suggests a very low impact angle (less than 10 degrees).

The long axis of the impact crater is viewed as the impacting direction of the projectile. Similar elliptical craters are observed elsewhere on Mars, as well as on our Moon.

The Spider, by Messenger

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

If you've followed this blog from the beginning, you were probably expecting a photo of Mars today, as we move outward through the Solar System away from the Sun. However, the Minister will occasionally interrupt his planned posts for breaking news and/or new images that are worthy of immediate attention. Such is the case today with a new photo of "the Spider," a geological feature on Mercury of an impact crater surrounded by numerous troughs pointing away from the crater, giving the impression of a very multi-legged spider:

The Narrow Angle Camera of the Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft obtained high-resolution images of the floor of the Caloris basin on January 14, 2008. Near the center of the basin, an area unseen by Mariner 10, this remarkable feature – nicknamed “the spider” by the science team – was revealed. A set of troughs radiates outward in a geometry unlike anything seen by Mariner 10. The radial troughs are interpreted to be the result of extension (breaking apart) of the floor materials that filled the Caloris basin after its formation. Other troughs near the center form a polygonal pattern. This type of polygonal pattern of troughs is also seen along the interior margin of the Caloris basin. An impact crater about 40 km (~25 miles) in diameter appears to be centered on “the spider.” The straight-line segments of the crater walls may have been influenced by preexisting extensional troughs, but some of the troughs may have formed at the time that the crater was excavated.

Apollo 17 at Taurus-Littrow, 1972

Credit: NASA

Like the Earth, a celestial body as unique as any other planet in our solar system, the Moon is far too often taken for granted by humanity. The Ministry for Space Exploration will post about the Moon as a celestial body, its past, present and future. While this blog cannot devote as much time to the Moon as it deserves, the Minister encourages readers to visit LPOD - Lunar Photo of the Day (the temporary site is located here) for more pictures and informative text about Earth's nearest celestial neighbor.

The above picture is of Harrison H. Schmitt of Apollo 17, who was photographed standing next to a huge, split boulder at the Taurus-Littrow landing site. Schmitt, who was a professional geologist, was also Apollo 17's lunar module pilot. After retiring from NASA, he served one term as a U.S. Senator from New Mexico.

This photograph was taken on December 13, 1972, by the Apollo 17 Commander, Astronaut Eugene A. Cernan.

Home

Credit: NASA (STS61A-34-0020)

While this blog will focus primarily on the solar system and beyond, the Ministry of Space Exploration won't neglect looking back at our own planet, which is a celestial body as interesting in its own right as any other. Just because we are most familiar with our world doesn't mean that we should take it for granted. This particular part of the Earth, the Finger Lakes region of upstate New York, has special meaning for the Minister of Space Exploration, as this is where he grew up. His hometown does not show on this particular image, but it's not too far from here, and he swam in two of the lakes shown above when he was a child, Keuka (which looks like a "U" on the left edge of the picture, although it's actually "Y" shaped) and Seneca (the lake to the right of Keuka). The Minister has not visited his hometown in over 20 years, but he would like to return there in the future, some day.

Individual agricultural fields are observable in this photograph of the two longest Finger Lakes—Seneca Lake (west) and Cayuga Lake (east). The smaller lake east of Cayuga Lake is Owasco Lake; the city of Auburn, New York, is located along the northern shore of Owasco Lake. While this region is known for general agriculture, dairying is extensive because of the close proximity to the dense population of the Mohawk River - Hudson River lowland from Buffalo to New York City. Grapes are also grown along the Finger Lakes where slopes ensure adequate air movement, which protects against frost, and where proximity to large water surfaces provides some ensurance against low temperatures.

This picture was taken by the crew of STS-61-A (Challenger) in October 1985.

Venus, by Venus Express

Credit: ESA © 2007 MPS/DLR-PF/IDA

This is a false-color image taken with the Venus Monitoring Camera (VMC) on board the European Space Agency's (ESA) Venus Express. It shows the full view of the southern hemisphere from the equator (right) to the pole. The south pole is surrounded by a dark oval feature. Moving to the right, away from the pole and towards the equator, we see streaky clouds, a bright mid-latitude band and mottled clouds in the convective sub-solar region.

This image was taken in the ultraviolet at 365 nanometers on 23 July 2007 as Venus Express was 35,000 km from the surface of the planet.

Are We There Yet?

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

This image demonstrates the first detection of Pluto using the high-resolution mode on the New Horizons Long-Range Reconnaissance Imager (LORRI). The mode provides a clear separation between Pluto and numerous nearby background stars. When the image was taken on October 6, 2007, Pluto was located in the constellation Serpens, in a region of the sky dense with background stars.

Typically, LORRI’s exposure time in hi-res mode is limited to approximately 0.1 seconds, but by using a special pointing mode that allowed an increase in the exposure time to 0.967 seconds, scientists were able to spot Pluto, which is approximately 15,000 times fainter than human eyes can detect.

New Horizons was still too far from Pluto (3.6 billion kilometers, or 2.2 billion miles) for LORRI to resolve any details on Pluto’s surface – that won’t happen until summer 2014, approximately one year before closest approach. For now the entire Pluto system remains a bright dot to the spacecraft’s telescopic camera, though LORRI is expected to start resolving Charon from Pluto – seeing them as separate objects – in summer 2010.

Mercury in Visible/Infrared Light, by Messenger

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters, in contrast to the two visible-light filters and one ultraviolet filter that were on Mariner 10's vidicon camera. By combining images taken through different filters in the visible and infrared, the MESSENGER data allow Mercury to be seen in a variety of high-resolution color views not previously possible. MESSENGER’s eyes can see far beyond the color range of the human eye, and the colors seen in the accompanying image are somewhat different from what a human would see.

The color image was generated by combining three separate images taken through WAC filters sensitive to light in different wavelengths; filters that transmit light with wavelengths of 1000, 700, and 430 nanometers (infrared, far red, and violet, respectively) were placed in the red, green, and blue channels, respectively, to create this image. The human eye is sensitive across only the wavelength range 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in the single-filter, black-and-white image released last week.

This visible-infrared image shows an incoming view of Mercury, about 80 minutes before MESSENGER's closest pass of the planet on January 14, 2008, from a distance of about 27,000 kilometers (17,000 miles).

Image sequences acquired through the 11 different MDIS filters are being used to distinguish subtle color variations indicative of different rock types. By analyzing color differences across all 11 filters, the MESSENGER team is investigating the variety of mineral and rock types present on Mercury’s surface. Such information will be key to addressing fundamental questions about how Mercury formed and evolved.

Mercury has a diameter of about 4880 kilometers (3030 miles), and the smallest feature visible in this color image is about 10 kilometers (6 miles) in size.

Mercury's Sholem Aleichem Crater, by Messenger

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The other day I wrote about the sense of humor the astronomers at APOD have. Now it's time to show some of the recent photos taken by the MESSENGER spacecraft that flew by the planet Mercury last week. This particular photo was taken last Monday, January 14th. The caption for the photo reads in part:

This image ... was acquired on January 14, 2008, 18:10 UTC, when the spacecraft was about 18,000 kilometers (11,000 miles) from the surface of Mercury, about 55 minutes before MESSENGER’s closest approach to the planet.

The image shows a variety of surface textures, including smooth plains at the center of the image, many impact craters (some with central peaks), and rough material that appears to have been ejected from the large crater to the lower right. This large 200-kilometer-wide (about 120 miles) crater was seen in less detail by Mariner 10 more than three decades ago and was named Sholem Aleichem for the Yiddish writer. In this MESSENGER image, it can be seen that the plains deposits filling the crater’s interior have been deformed by linear ridges. The shadowed area on the right of the image is the day-night boundary, known as the terminator.

One interesting fact that APOD pointed out is that many of the craters on Mercury are shallower than comparable craters on the Moon, the reason being the higher gravitational pull on Mercury, which "helps flatten tall structures like high crater walls."

As for Sholem Aleichem: He was a Russian Jewish writer (1859-1916) whose stories about Tevye the Milkman became the basis for the musical and film "Fiddler on the Roof."