The South Rim of Aristarchus

LROC view looking obliquely of the south rim of Aristarchus from the west (NASA/GSFC/Arizona State University)

Flying over at an altitude of 135 km, NASA’s Lunar Reconnaissance Orbiter captured this lovely oblique view of the crater Aristarchus, looking down at the 40-km (25-mile) -wide crater’s southern rim from the west.

The broad flank of Aristarchus’ 300-meter (980-foot) central peak and surrounding hills can be seen at left, casting lengthening shadows in the setting sun.

Named after the Greek astronomer who first proposed a controversial heliocentric model for the Solar System in the 3rd century BCE, Aristarchus is a prominent crater located near the Moon’s northwestern limb within the geologically-diverse Oceanus Procellarum — the “Ocean of Storms.” Surrounded by rays of bright ejecta that extend down its stepped rim, the floor of Aristarchus drops 3.7 km (2.3 miles) below the surrounding lunar landscape.

Read more: LRO Lets You Stand on the Rim of Aristarchus Crater

The bright material seen in the ejecta streaks seems to echo the patterns of light and dark material lining the slopes of Aristarchus’ central peak, suggesting that they may be the made of similar material.


Detail of the 4.5-km-long central peak of Aristarchus (NASA/GSFC/Arizona State University)

The impact that created Aristarchus an estimated 450 million years ago excavated subsurface material, melting and spraying it tens of kilometers over the surrounding plateau. It’s thought that the central peak is likely composed of the same stuff, dredged up by the impact and frozen in place.

Future lunar explorers, should they ever visit this region, would be able to collect samples from the base of the central peak and compare them to samples from the bright rays to see if they match up, allowing researchers to learn about the composition of the material underlying the plateau from rocks scattered conveniently around the surface… this is the beauty of such (relatively) recent craters! The digging’s already been done for us.

Read more about this on Arizona State University’s LROC site and explore a zoomable version of the original NAC frame here.

Lighting Up Mercury’s Shadowy North Pole

Part of a stereographic projection of Mercury’s north pole

Talk about northern exposure! This is a section of a much larger image, released today by the MESSENGER team, showing the heavily-cratered north pole of Mercury as seen by the MESSENGER spacecraft’s Mercury Dual Imaging System (MDIS) instrument.

See the full-size image below:

Many MDIS images were averaged together to create a mosaic of Mercury’s polar region, which this stereographic projection is centered on. MESSENGER is at its lowest altitude as it passes over Mercury’s northern hemisphere — about  200 kilometers (124 miles), which is just a little over half the altitude of the ISS.

The largest centrally-peaked crater near the center is Prokofiev, named after a 20th-century Russian composer. Approximately 110 km (68 mi.) in diameter, its permanently-shadowed interior is home to radar-bright deposits that are thought to contain water ice.

Even though Mercury is almost three times closer to the Sun than Earth is and hosts searing daytime temperatures of 425ºC (800ºF), there’s virtually no atmosphere to hold or transmit that heat. Nighttime temperatures can reach as low as -185ºC (-300ºF), and since a day on Mercury is 176 Earth days long it gets very cold for quite a long time!

Also, because Mercury’s axis of rotation isn’t tilted like Earth’s, low elevation areas near the poles receive literally no sunlight. Unless vaporized by a meteorite impact any ice gathered inside these deep craters would remain permanently frozen.

Here’s an orthographic projection of the image above, showing what the scene would look like on Mercury — that is, if it was ever fully lit by the Sun, which it isn’t.

Many of the craters on Mercury’s north pole have recently been named after famous artists, authors and composers, such as Kandinsky, Stieglitz, Goethe, and even one named after J.R.R. Tolkien. You can see an annotated image showing the names of Mercury’s north polar craters here.

Read More: “The Hobbit” Author Gets a Crater on Mercury

On November 29, NASA will host a news conference at 2 p.m. EST to reveal new observations from MESSENGER, the first spacecraft to orbit Mercury. The news conference will be carried live on NASA Television and the agency’s website… you can tune in on NASA TV here. 

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

Mercury’s Surface is Full of Sulfur

The southern portion of Mercury’s Vivaldi basin and outlying rugged terrain

Named for the 17th-century Venetian composer, the southern half of Mercury’s Vivaldi basin is seen in this image acquired on August 26 by NASA’s MESSENGER spacecraft. The 213-km (132-mile) -wide crater’s smooth floor is contrasted by the incredibly rugged terrain beyond its outermost ring — a result of the ejected material that was flung out from the impact site and emphasized by the low angle of illumination.

The floor of the crater remained relatively smooth due to molten material that erupted in the wake of the impact event, flooding the basin.

Recent findings from the MESSENGER mission have revealed variations in Mercury’s surface composition due to volcanism that occurred at different times, as well as a surprising concentration of elements like magnesium and sulfur — much more so than any of the other terrestrial planets.

In results to be published in the Journal of Geophysical Research, scientists report that Mercury’s volcanic smooth plains differ in composition from older surrounding terrains. The older terrain has higher ratios of magnesium to silicon, sulfur to silicon, and calcium to silicon, but lower ratios of aluminum to silicon, suggesting that the smooth plains material erupted from a magma source that was chemically different from the source of the material in the older regions, according to Shoshana Weider of the Carnegie Institution of Washington, the lead author on the paper.

Mercury’s surface was also found to be high in magnesium and sulfur-enriched minerals.

“None of the other terrestrial planets have such high levels of sulfur. We are seeing about ten times the amount of sulfur than on Earth and Mars,” Weider said. “In terms of magnesium, we do have some materials on Earth that are high in magnesium. They tend to be ancient volcanic rocks that formed from very hot lavas. So this composition on Mercury tells us that eruptions of high-temperature lavas might have formed these high-magnesium materials.”

Read: MESSENGER Reveals Mercury’s Colors

The data was gathered with MESSENGER’s X-Ray Spectrometer (XRS) — one of two instruments designed to measure the abundances of many key elements in the top 2mm of Mercury’s crust. XRS detects emissions from elements in the 1-10 kiloelectron-volt (keV) range – specifically, magnesium, aluminum, silicon, sulfur, calcium, titanium, and iron.

Read more on the MESSENGER mission site here.

Inset image: A global mosaic of Mercury from MESSENGER (2011). Image credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

“The Hobbit” Author Gets a Crater on Mercury

Here’s a little something to please fans of space, art and fantasy alike (and those who enjoy all three): on August 6 the International Astronomical Union approved names for 9 craters on Mercury, one of which is named for J.R.R. Tolkien, revered author of The Hobbit and The Lord of the Rings (among other seminal fantasy works.)

The crater Tolkien is approximately 30 miles (48 km) in diameter. All 9 newly-named craters are located in Mercury’s north polar region and exhibit radar evidence of water ice hidden in their shadowy pocketses.

IAU procedure for craters on Mercury has them named after “deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field and have been recognized as art historically significant figures for more than 50 years.” Find out who all 9 new craters are named for after the jump:

Egonu, for Uzo Egonu (1931-1996), a Nigerian-born painter who at 13 was sent to England to study art, first at a private school in Norfolk and later at the Camberwell School of Arts and Crafts. Exile, alienation, and the pain of displaced peoples were recurrent themes in his work.

Gaudí­, after Antoni Gaudí­ (1852-1926), a Spanish architect whose work concentrated largely on the Catalan capital of Barcelona. He was very skilled with ceramics, stained glass, wrought-iron forging, and carpentry and integrated these crafts into his architecture.

Kandinsky, for Wassily Kandinsky (1866-1944), a Russian painter and art theorist credited with painting the first purely abstract works.

Petronius, for Titus Petronius (c. AD 27-66), a Roman courtier during the reign of Nero. He is generally believed to be the author of the Satyricon, a satirical novel believed to have been written during the Neronian era.

Prokofiev, for Sergei Prokofiev (1891-1953), a Russian composer, pianist, and conductor who is considered one of the major composers of the 20th century. His best-known works include the ballet Romeo and Juliet — from which “Dance of the Knights” is taken — and Peter and the Wolf.

Tolkien, for John Ronald Reuel (J. R. R.) Tolkien (1892-1973), an English writer, poet, philologist, and university professor, best known as the author of the classic fantasy novels The Hobbit and The Lord of the Rings.

Tryggvadóttir, for Nina Tryggvadóttir (1913-1968), one of Iceland’s most important abstract expressionist artists and one of very few Icelandic female artists of her generation. She primarily worked in painting, but she also created collages, stained glass work, and mosaics.

Qiu Ying, for Shifu Qiu Ying (1494-1552), a Chinese painter who specialized in the gongbi brush technique, a careful realist method in Chinese painting. He is regarded as one of the Four Great Masters of the Ming Dynasty.

Yoshikawa, for Eiji Yoshikawa (1892-1962), a Japanese historical novelist best known for his revisions of older classics including The Tale of the Heike, Tale of Genji, Outlaws of the Marsh, and Romance of the Three Kingdoms.

“These designations expand the opportunities to recognize the contributions to the arts by the most creative individuals from many cultures and eras. The names of those individuals are now linked in perpetuity to the innermost planet.”

– Sean Solomon, MESSENGER Principal Investigator

The craters were imaged by NASA’s MESSENGER spacecraft, currently in extended mission around Mercury. Learn more about the preciousss MESSENGER mission here. (Gollum! Gollum!)

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

Postcards From The (Inner) Edge

As the world turns its gaze outward in anticipation of the arrival of Mars Science Laboratory — with its hair-raising “seven minutes of terror” landing — let’s take a moment to look back inward, where MESSENGER is still faithfully orbiting the first rock from the Sun, Mercury, and sending back images that could only have been imagined just a few years ago.

The image above shows the graben-gouged terrain around Balanchine crater, within Mercury’s vast Caloris Basin impact crater. Named for the co-founder of the New York City Ballet, Balanchine crater is 41 km (25.5 miles) in diameter and filled with the curious erosion features known as hollows. Graben — basically sunken troughs in the surface — are the result of extensional forces that have pulled sections of the planet’s upper crust apart.

This image shows the peak-ring structure located within the much larger crater Rustaveli, which is 180 km (112 miles) in diameter. One of the more recently-named craters (the IAU convention for new features on Mercury has them titled after renowned artists, writers and composers from history) Rustaveli is named for a 12th-century Georgian poet who wrote the epic “The Knight in the Panther’s Skin”. The crater that now bears his namesake is located on Mercury’s northern hemisphere.

These two craters — also located within Caloris Basin — don’t yet have names but are no less interesting. Their overlapping positions works like an optical illusion, making the newer,sharper-edged crater on the right seem to almost float above the surface. The false-color of the image highlights the difference in surface composition of the two craters, which are both about 40 km (24 miles) wide. (The Caloris Basin in which they reside, however, is one of the largest known impact sites in our solar system, measuring at 1550 km — 963 miles — across!)

Now we zoom out for a wider view of our solar system’s second-densest planet (Earth is the first) and take a look at an image that’s night and day — literally! This is Mercury’s terminator, the twilit dividing line between night and day. More than just making a pretty picture, data on this transition is valuable to scientists as some atmospheric phenomena can only be observed at the terminator, such as the interaction between surface dust and charged particles from the Sun (which, at less than half the distance to the Sun than we are, Mercury is constantly bathed in.)

And now to zoom back in, we get a good look at an unnamed central-peaked crater about 85 km (52 miles) across in an oblique view  that highlights the hollows and depressions within its floor. Acquired as part of what’s called a “targeted observation”, high-resolution images like this (79 meters/pixel) allow scientists to closely investigate specific features — but sadly there’s just not enough mission time to image all of Mercury at this level of detail.

On March 17, 2011 (March 18, 2011, UTC), MESSENGER became the first spacecraft ever to orbit Mercury. The mission has provided the first data from Mercury since Mariner 10, over 30 years ago. After over 1,000 orbits, 98 percent of Mercury is now imaged in detail, allowing us to know more about our solar system’s innermost world than ever before.

Keep up with MESSENGER updates (and the latest images) on the mission website here.

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

An Epic Crater Called Odysseus

On June 28 NASA’s Cassini spacecraft passed by Tethys, a 1,062-kilometer (662-mile) -wide moon of Saturn that’s made almost entirely of ice. Tethys is covered in craters of all sizes but by far the most dramatic of all is the enormous Odysseus crater, which spans an impressive 450 kilometers (280 miles) of the moon’s northern hemisphere — nearly two-fifths of its entire diameter!

In fact, whatever struck Tethys in the distant past probably should have shattered it into pieces… but didn’t.

Tethys likely held itself together because when the impact occurred that formed Odysseus, the moon was still partially molten. It was able to absorb some of the energy of the impact and thus avoid disintegration — although it was left with a quite the battle scar as an eternal reminder.

The images below are raw images from Cassini’s latest pass of Tethys, showing the moon’s rugged terrain and portions of Odysseus from a distance of 68,521 kilometers (42,577 miles).

The central peak of Odysseus has collapsed, leaving a depression — another indication that the moon wasn’t entirely solid at the time of impact.

Tethys orbits Saturn at a distance of 294,660 kilometers (183,100 miles), about 62,000 miles closer than the Moon is from Earth. Such a close proximity to Saturn subjects Tethys to tidal forces, the frictional heating of which likely helped keep it from cooling and solidifying longer than more distant moons. As a result Tethys appears somewhat less cratered than sister moons Rhea and Dione, which still bear the marks of their earliest impacts… although looking at the region south of Odysseus it’s hard to image a more extensively-cratered place.

Tethys is just another reminder of the violent place our solar system can be. Find out more about Tethys on the Cassini mission site here.

Image credits: NASA/JPL/Space Science Institute. Edited by J. Major. Images have not been calibrated or validated, and each has been level-adjusted and sharpened to bring out surface detail, and in some areas deinterlacing was used to remove linear raw image artifacts.

Exploration at its Finest: Cassini Visits Dione


After completing its most recent flyby of Enceladus, Cassini made a pass by Dione — its final visit of the icy moon for the next three years. Coming within  5,000 miles (8000 km) of Dione on May 2, Cassini captured some fantastic images of the moon’s heavily-cratered and frozen surface. Here’s just a few of the raw images that arrived back here on Earth earlier today:

Crescent-lit Dione, with some reflected light via Saturnshine
A nearly fully-lit Dione, with Saturn's rings in the background
Dione's extensively-cratered limb
Some of Dione's signature "wispy lines", bright icy faces of sheer cliffs now known to be tectonic in origin
A color-composite image of an ancient impact crater on the edge of Dione's Saturn-facing side - this could be from the impact that spun the moon 180 degrees. (NASA/JPL/SSI/J. Major)

698 miles (1123 km) in diameter, Dione orbits Saturn at about the same distance that the Moon orbits Earth. Its composition is two-thirds water ice, which at the incredibly cold temperatures found around Saturn behaves like rock does here on Earth.


Cassini won’t visit Dione so closely again until June 2015, after spending three years angled high out of the equatorial plane while it studies Saturn’s rings and polar regions.

As Carolyn Porco, Cassini Imaging Team Leader said today, “This is exploration at its finest. It won’t continue forever. So, enjoy it while it lasts!”

See more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site here.

Image credits: NASA/JPL/Space Science Institute 


Scientists Suggest Evidence of Recent Lunar Volcanism

There may be a volcanic vent on the central peak of Tycho crater, according to an Indian research team. (Image: NASA Goddard/Arizona State University)


A team of researchers at India’s Physical Research Laboratory (PRL) claims it has found evidence of relatively recent volcanic activity on the Moon, using data from NASA’s Lunar Reconnaissance Orbiter and the Chadrayaan-1 spacecraft. According to the findings the central peak of Tycho crater contains features that are volcanic in origin, indicating that the Moon was geologically active during the crater’s formation 110 million years ago.

In an article by the Deccan Herald, a Bangalore-based  publication, the PRL researchers claim that vents, lava channels and solidified flows of inner crustal material found within Tycho were made as recently as 100 million years ago — after the creation of the crater.

This could indicate that there was pre-existing volcanic activity within the Moon at the site of the Tycho impact, lending credence to the idea that the Moon was recently geologically active.

In addition, large boulders ranging in size from 33 meters to hundreds of yards across have been spotted on Tycho’s central peaks by LRO, including one 400-foot (120-meter) -wide specimen nestled atop the highest summit. How did such large boulders get there and what are they made of?

A 400-foot-wide boulder within the central peak of Tycho. (NASA/GSFC/LROC)

The researchers hint that they may also be volcanic in origin.

“A surprise findings revealed the  presence of large boulders–about 100 meter in size –on top of the peak. Nobody knew how did they reach the top,” said Prakash Chauhan, a PRL scientist.

Without further studies it’s difficult to determine the exact origin and ages of these lunar formations. The team awaits future research by Chandrayaan-II, which will examine the Moon from orbit as well as land a rover onto the lunar surface. Chandrayaan-II is expected to launch in early 2014.

The PRL team’s findings were published in the April 10 issue of Current Science.

Read the article in the Deccan Herald here.


The scarp-filled Donne crater on Mercury


Named after the 17th-century metaphysical poet, Mercury’s Donne crater was captured in this image by NASA’s MESSENGER spacecraft. The 53-mile (83-km) -wide crater features a large, rounded central peak and numerous lobate scarps lining its floor.

Lobate scarps are found all across Mercury. Visible above as arc-shaped ridges, they are most likely thrust faults resulting from surface compression and contraction.

Donne’s central peak has been well-eroded by impacts into a softly rolling mound. Central peaks are common features of larger craters, thought to be formed when the excavation of material during an impact springs the crater floor upwards — a process called “isostatic rebound”.

This image was acquired by MESSENGER’s Narrow-Angle Camera (NAC) on August 2, 2011.

On March 17 MESSENGER successfully wrapped up a year-long campaign to perform the first complete reconnaissance of the geochemistry, geophysics, geologic history, atmosphere, magnetosphere, and plasma environment of Mercury. The following day, March 18, marked the official start of its extended phase designed to build upon those discoveries.

“Six plus years of cruise operations, capped by a year of nearly flawless orbital operations, with an additional year of scientific return ahead in the harsh environment at 0.3 astronomical units (27,886,766 miles) from the Sun,” said MESSENGER Mission Systems Engineer Eric Finnegan at JHU/APL. All this “achieved with a 1,000 kg satellite, designed, built, and launched in less than four years for a total mission cost of less than $450 million.”

Well “Donne”, MESSENGER!

Read more about the MESSENGER mission’s extension here.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

A Peek at a Pitch-Black Pit

A rimless pit crater within the crater Tolstoj


MESSENGER captured this high-resolution image of an elongated pit crater within the floor of the 355-km (220-mile) -wide crater Tolstoj on Mercury on Jan. 11, 2012. The low angle of sun illumination puts the interior of the pit crater into deep shadow, making it appear bottomless.

Pit craters are not caused by impacts, but rather by the collapse of the roof of an underground magma chamber. They are characterized by the lack of a rim or surrounding ejecta blankets, and are often not circular in shape.

Since the floor of Tolstoj crater is thought to have once been flooded by lava, a pit crater is not out of place here.

The presence of such craters on Mercury indicates past volcanic activity on Mercury contributing to the planet’s evolution.

Read more on the MESSENGER mission website here.

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