The news of extraterrestrial meteor showers on Mercury came out of the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society currently underway this week in National Harbor, Maryland. The study was carried out by Rosemary Killen of NASA’s Goddard Spaceflight Center, working with Matthew Burger of Morgan State University in Baltimore, Maryland and Apostolos Christou from the Armagh Observatory in Northern Ireland. The study looked at data from the MErcury Surface Space Environment Geochemistry and Ranging (MESSENGER) spacecraft, which orbited Mercury until late April of this year. Astronomers published the results in the September 28th issue of Geophysical Research Letters.
Micrometeoroid debris litters the ecliptic plane, the result of millions of years of passages of comets through the inner solar system. You can see evidence of this in the band of the zodiacal light visible at dawn or dusk from a dark sky site, and the elusive counter-glow of the gegenschein.
Researchers have tagged meteoroid impacts as a previous source of the tenuous exosphere tails exhibited by otherwise airless worlds such as Mercury. The impacts kick up a detectable wind of calcium particles as Mercury plows through the zodiacal cloud of debris.
“We already knew that impacts were important in producing exospheres,” says Killen in a recent NASA Goddard press release. “What we did not know was the relative importance of comet streams over zodiacal dust.”
This calcium peak, however, posed a mystery to researchers. Namely, the peak was occurring just after perihelion—Mercury orbits the Sun once every 88 Earth days, and travels from 0.31 AU from the Sun at perihelion to 0.47 AU at aphelion—versus an expected calcium peak predicted by researchers just before perihelion.
A key suspect in the calcium meteor spike dilemma came in the way of periodic Comet 2P Encke. Orbiting the Sun every 3.3 years—the shortest orbit of any known periodic comet—2P Encke has made many passages through the inner solar system, more than enough to lay down a dense and stable meteoroid debris stream over the millennia.
With an orbit ranging from a perihelion at 0.3 AU interior to Mercury’s to 4 AU, debris from Encke visits Earth as well in the form of the November Taurid Fireballs currently gracing the night skies of the Earth.
The Encke connection still presented a problem: the cometary stream is closest to the orbit of Mercury about a week later than the observed calcium peak. It was as if the stream had drifted over time…
Enter the Poynting-Robertson effect. This is a drag created by solar radiation pressure over time. The push on cometary dust grains thanks to the Poynting-Robertson effect is tiny, but it does add up over time, modifying and moving meteor streams. We see this happening in our own local meteor stream environment, as once great showers such as the late 19th century Andromedids fade into obscurity. The gravitational influence of the planets also plays a role in the evolution of meteor shower streams as well.
Researchers in the study re-ran the model, using MESSENGER data and accounting for the Poynting-Robertson effect. They found the peak of the calcium emissions seen today are consistent with millimeter-sized grains ejected from Comet Encke about 10,000 to 20,000 years ago. That grain size and distribution is important, as bigger, more massive grains result in a smaller drag force.
This finding shows the role and mechanism that cometary debris plays in exosphere production on worlds like Mercury.
“Finding that we can move the location of stream to match MESSENGER’s observations is gratifying, but the fact that the shift agrees with what we know about Encke and its stream from independent source makes us confident that the cause-and-effect relationship is real, says Christou in this week’s NASA Goddard press release.
Launched in 2004, MESSENGER arrived at Mercury in March 2011 and orbited the world for over four years, the first spacecraft to do so. MESSENGER mapped the entire surface of Mercury for the first time, and became the first human-made artifact to impact Mercury on April 30th, 2015.
The joint JAXA/ESA mission BepiColombo is the next Mercury mission in the pipeline, set to leave Earth on 2017 for insertion into orbit around Mercury on 2024.
An interesting find on the innermost world, and a fascinating connection between Earth and Mercury via comet 2P Encke and the Taurid Fireballs.
Don’t take these spectacular Mercury images (below the jump) for granted. Three weeks ago, NASA’s orbiting Mercury spacecraft did an engine fire to boost its altitude above the hothouse planet. Another one is scheduled for January.
But all this will do is delay the end of the long-running mission — the first one to orbit Mercury — until early 2015, the Johns Hopkins Applied Physics Laboratory wrote in an update. These maneuvers “extend orbital operations and delay the probe’s inevitable impact onto Mercury’s surface until early next spring,” the organization said in a statement.
Until MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) flew by Mercury for the first time in January 2008, we knew very little about the planet. The only close-up pictures previously came from Mariner 10, which whizzed by a few times in 1974-75. After a few flybys, MESSENGER settled into orbit in 2011.
Mercury’s high density compared to other planets remains a mystery. MESSENGER investigations found a surface that didn’t have a lot of iron in it, but lots of volatile materials such as sodium and sulfur.
The surface had volcanoes on it and still has water ice in permanently shadowed craters near the poles.
Its magnetic field produces weird effects that are still being examined. NASA speaks of “unexplained bursts of electrons and highly variable distributions of different elements” in its tenuous atmosphere, called an exosphere.
“Our only regret is that we have insufficient propellant to operate another 10 years, but we look forward to the incredible science returns planned for the final eight months of the mission,” stated Andy Calloway, MESSENGER mission operations manager at the Johns Hopkins University Applied Physics Laboratory, at the time.
MESSENGER has done several orbital-boosting maneuvers in recent months to prolong the mission as possible. The first one in June adjusted its orbit to between 71.4 miles (115 kilometers) and 97.2 miles (156.4 kilometers), while the second in September went lower: a minimum of 15.7 miles (25.2 kilometers) to 58.2 miles (93.7 kilometers).
New pictures of water ice at Mercury’s north pole — the first such optical images ever — could help scientists better understand how water came to planets in the rest of the Solar System, including Earth. The image you see above came courtesy of NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.
Mercury is a hot planet (it’s the closest one to the Sun), so the only way the ice survives is in deep shadow. This makes it hard to spot unless scientists use some clever techniques. In this case, they examined some scattered light from Prokofiev, the biggest crater in Mercury’s north pole suspected to hold the deposits.
The pictures show that Prokofiev’s surface water ice likely arrived after the craters underneath. And in an intriguing find, there is probably other water ice sitting under dark materials believed to be “frozen organic-rich compounds,” stated the Johns Hopkins University Applied Physics Laboratory.
“This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury’s poles are geologically young, relative to the time scale for lateral mixing by impacts,” stated lead researcher Nancy Chabot, the Instrument Scientist for MESSENGER’s Mercury dual imaging system.
“One of the big questions we’ve been grappling with is ‘When did Mercury’s water ice deposits show up?’ Are they billions of years old, or were they emplaced only recently?”, added Chabot, who is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Maryland. “Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth.”
Another intriguing property comes when scientists compare Mercury to the Moon: because the ice looks different on both relatively atmosphere-less bodies, scientists believe the water came more recently to the Moon. But more study is required.
Exactly 40 Years ago today on Feb. 5, 1974, Mariner 10, accomplished a history making and groundbreaking feat when the NASA science probe became the first spacecraft ever to test out and execute the technique known as a planetary gravity assisted flyby used to alter its speed and trajectory – in order to reach another celestial body.
Mariner 10 flew by Venus 40 years ago to enable the probe to gain enough speed and alter its flight path to eventually become humanity’s first spacecraft to reach the planet Mercury, closest to our Sun.
Indeed it was the first spacecraft to visit two planets.
During the flyby precisely four decades ago, Mariner 10 snapped its 1st close up view of Venus – see above.
From that moment forward, gravity assisted slingshot maneuvers became an extremely important technique used numerous times by NASA to carry out planetary exploration missions that would not otherwise have been possible.
For example, NASA’s twin Voyager 1 and 2 probes launched barely three years later in 1977 used the gravity speed boost to conduct their own historic flyby expeditions to our Solar Systems outer planets.
Without the flyby’s, the rocket launchers thrust by themselves did not provide sufficient interplanetary speed to reach their follow on targets.
NASA’s Juno Jupiter orbiter just flew back around Earth this past October 9, 2013 to gain the speed it requires to reach the Jovian system.
The Mariner 10 probe used an ultraviolet filter in its imaging system to bring out details in the Venusian clouds which are otherwise featureless to the human eye – as you’ll notice when viewing it through a telescope.
Venus surface is completely obscured by a thick layer of carbon dioxide clouds.
The hellish planet’s surface temperature is 460 degrees Celsius or 900 degrees Fahrenheit.
Following the completely successful Venus flyby, Mariner 10 eventually went on to conduct a trio of flyby’s of Mercury in 1974 and 1975.
It imaged nearly half of the planets moon-like surface, found surprising evidence of a magnetic field, discovered that a metallic core comprised nearly 80 percent of the planet’s mass, and measured temperatures ranging from 187°C on the dayside to minus 183°C on the nightside.
Mercury was not visited again for over three decades until NASA’s MESSENGER flew by and eventually orbited the planet – and where it remains active today.
Mariner 10 was launched on Nov. 3, 1973 from the Kennedy Space Center atop an Atlas-Centaur rocket.
Shortly after blastoff if also took photos of the Earth and the Moon.
Ultimately it was the last of NASA’s venerable Mariner planetary missions hailing from the dawn of the Space Age.
Mariner 11 and 12 were descoped due to congressional budget cuts and eventually renamed as Voyager 1 and 2.
The Mariner 10 science team was led by Bruce Murray of the Jet Propulsion Laboratory (JPL), Pasadena, Calif.
Murray eventually became the Director of JPL. After he passed away in 2013, key science features on Martian mountain climbing destinations were named in his honor by the Opportunity and Curiosity Mars rover science teams.
Stay tuned here for Ken’s continuing LADEE, Chang’e-3, Orion, Orbital Sciences, SpaceX, commercial space, Mars rover and more planetary and human spaceflight news.
After two years of doing the loop-the-loop around Mercury, MESSENGER has unveiled a bunch of surprises from Mercury — the closest planet to the Sun.
The spacecraft launched in 2004 and made three flybys of the planet before settling into orbit two years ago today. Incredibly, MESSENGER is only the second NASA probe to visit Mercury; the first one, Mariner 10, only flew by a few times in the 1970s. It was an incredible feat for the time, but we didn’t even have a complete map of Mercury before MESSENGER arrived at the planet.
So, what have scientists found in MESSENGER’s two years in orbit? Tales of sulfur, organic materials and iron, it turns out.
Mercury’s south pole has a weak spot
The magnetic field lines converge differently at the north and south poles of Mercury. What does this mean? There’s a larger “hole” at the south pole for charged particles to do their thing to the surface of Mercury. At the time this information was released, NASA said it’s possible that space weathering or erosion would be different at the north and south poles because of this. Charged particles on the surface would also add to Mercury’s wispy atmosphere.
How the atmosphere changes according to distance from the sun
Wondering about the atmosphere on Mercury? It depends on the season, and also the element. The scientists found striking changes in calcium, magnesium and sodium when the planet was closer to and further from the sun.
“A striking illustration of what we call ‘seasonal’ effects in Mercury’s exosphere is that the neutral sodium tail, so prominent in the first two flybys, is 10 to 20 times less intense in emission and significantly reduced in extent,” said participating scientist Ron Vervack, of the Johns Hopkins University Applied Physics Laboratory in 2009. “This difference is related to expected variations in solar radiation pressure as Mercury moves in its orbit and demonstrates why Mercury’s exosphere is one of the most dynamic in the solar system.”
Discovery of water ice and organics
Late in 2012, NASA finally was able to corroborate some science results from about 20 years ago. Scientists on Earth saw “radar bright” images from Mercury in the 1990s, implying that there was ice and organic materials at the poles. MESSENGER finally confirmed that through three separate lines of investigation that were published in Science in 2012. Scientists estimated the planet holds between 100 billion and 1 trillion tons of water ice, perhaps as deep as 20 meters in some places. “Water ice passed three challenging tests and we know of no other compound that matches the characteristics we have measured with the MESSENGER spacecraft,” said MESSENGER principal investigator Sean Solomon in a NASA briefing.
Mercury has a big iron core
While scientists knew before that Mercury has an iron core, the sheer size of it surprised scientists. At 85%, the proportion of the core to the rest of the planet dwarfs its rocky solar system companions. Further, scientists measured Mercury’s gravity. From that, they were surprised to see that the planet had a partially liquid core. “The planet is sufficiently small that at one time many scientists thought the interior should have cooled to the point that the core would be solid,” stated Case Western Reserve University’s Steven A. Hauck II, a co-author of a paper on the topic that appeared in Science Express.
The surface is sulfur-rich
At some point in Mercury’s history, it’s possible that it could have had lavas erupt and sprinkle the surface with sulfur, magnesium and similar materials. At any rate, what is known for sure is there is quite a bit of sulfur on Mercury’s surface. “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,” said paper author Shoshana Weider of the Carnegie Institution of Washington.
The history of astronomy is littered with astronomical objects in the solar system that have fallen to the wayside. These include fleeting sightings of Venusian moons, inter-mercurial planets, and even secondary moons of the Earth.
While none of these observations ever amounted to true discoveries, this weekend gives observers and astrophotographers a unique chance to “mimic” a spurious discovery that has dotted astronomical lore: a visual “pseudo-moon” for the planet Mercury. This “moon illusion” will occur on February 8, 2013 during the closest conjunction of two naked eye planets in 2013. February offers a chance to see the fleeting Mercury in the sky, and this conjunction with Mars will provide the opportunity to see how Mercury would look in the night sky if it had a moon!
Mercury has been suspected of having moons before. On March 29th 1974, the Mariner 10 spacecraft became the first mission to image the innermost world up close. Mariner 10 mapped 40-45% of Mercury on 3 successive passes, revealing a pock-marked world not that different than our own Moon. But Mariner 10 also detected something more: brief anomalies in the ultra-violet spectrum suggestive of a moon with a 3 day period. For a very brief time, Mercury was thought to have a moon of its own, and NASA nearly made a press release to this effect. The spectroscopic binary 31 Crateris is now suspect in the anomalous readings. Still, the Mariner 10 observation made researchers realize the observations in the extreme UV were possible over interstellar distances.
Today, NASA has a permanent emissary orbiting Mercury with its MESSENGER spacecraft. MESSENGER first entered orbit around Mercury on March 18th, 2011 after a series of trajectory changing flybys. MESSENGER has filled in the map of the remainder of Mercury’s surface, with no signs of the anomalous “moon.” Interestingly, MESSENGER was also on the lookout for “Vulcanoids” (tiny asteroids interior to Mercury’s orbit; sorry, Mr. Spock) while enroute to its final orbital insertion. NASA even released an April Fool’s Day prank of a fake “discovery” of a Mercurial moon dubbed Caduceus in 2012.
But MESSENGER has made some fascinating true to life discoveries, such as sampling Mercury’s tenuous exosphere & the possibility of ice at its permanently shadowed poles. Lots of new features have been mapped and named on Mercury, following the convention of naming features after famous deceased artists, musicians and authors set forth by the International Astronomical Union. It’s amazing to think that we had no detailed views at the entire surface of Mercury until the 1970’s, although some ground-based professional observatories and even skilled amateurs are now doing just that.
Fast forward to this weekend. Mercury is just beginning its first apparition of six in 2013 this week and is currently visible low in the dusk sky after sunset to the west. Mercury reaches greatest eastern elongation on February 16th at 18.1° from the Sun. Interestingly, that’s very close to the shortest elongation that can occur. Mercury’s orbit is eccentric enough that greatest elongation as seen from the Earth can vary from 17.9° to 27.8°. This month’s elongation happens within only 5 hours of Mercury reaching perihelion at 46 million kilometers from the Sun. This means that Mercury won’t peak above the dusk horizon for mid-northern latitude observers quite as high as it will during the next evening apparition of the planet in June.
This appearance of Mercury does, however, have some things going for it. First off, the ecliptic sits at a favorable viewing angle, roughly perpendicular to the western horizon at dusk for mid- to high northern latitude observers. This gives Mercury a bit of a “boost” out of the weeds. Secondly, Mercury is a full magnitude (2.512 times) brighter when it reaches maximum elongation near perihelion than aphelion, such as its next appearance in the dawn sky on March 31st of this year. Mercury will reach magnitude -0.5, versus +0.5 in late March.
To see Mercury, find a site with a western horizon free of ground clutter and start sweeping the horizon with binoculars about 15 minutes after local sunset. See a reddish dot just above Mercury? That’s the planet Mars, shining about 7 times fainter than -1.0 magnitude Mercury at magnitude +1.2. Mercury is fast approaching a conjunction with Mars; the two will be only 15’ apart (half the average width of a Full Moon) on the evening of February 8th at 17:00 Universal Time!
If you ever wondered how Mercury would appear with a moon, now is a good time to take a look! Again, binoculars are the best optical tool for the job. Can you see both with the naked eye? Can you place both in the same low power field of view with a telescope? You’ll only have a 15-30 minute window (depending on latitude) to snare the pairing before they follow the setting Sun below the horizon. Photographing the pair will be tricky, though not impossible, as they present a very low contrast against the bright background twilight sky.
Don’t expect to see detail on Mercury or Mars telescopically; Mercury only appears 5.8” across on the 8th, while Mars is 4” in apparent size. Mars disappears from view later this month to reach solar conjunction on April 18th 2013. The waxing crescent Moon just 1 day after New joins the pair on the evenings of February 10th and 11th.
Now for the “Wow” factor of what you’re seeing. The conjunction of Mars and Mercury only appears close; in reality, they are over 180 million kilometers apart. Mercury is 1.15 Astronomical Units (A.U.s)/178 million kilometers from us on February 8th, while Mars is nearly at its farthest from us at 2.31 A.U.s/358 million kilometers distant. It’s splendid to think that with Curiosity and friends operating on Mars and Messenger orbiting Mercury, we now have permanent robotic “eyes” on and around both!
Credits: Simulation created by the author using Starry Night.
A year ago, 2011 was proclaimed as the “Year of the Solar System” by NASA’s Planetary Science division. And what a year of excitement it was indeed for the planetary science community, amateur astronomers and the general public alike !
NASA successfully delivered astounding results on all fronts – On the Story of How We Came to Be.
“2011 was definitely the best year ever for NASA Planetary Science!” said Jim Green in an exclusive interview with Universe Today. Green is the Director of Planetary Science for the Science Mission Directorate at NASA HQ. “The Search for Life is a significant priority for NASA.”
This past year was without doubt simply breathtaking in scope in terms of new missions, new discoveries and extraordinary technical achievements. The comprehensive list of celestial targets investigated in 2011 spanned virtually every type of object in our solar system – from the innermost planet to the outermost reaches nearly touching interplanetary space.
There was even a stunningly evocative picture showing “All of Humanity” – especially appropriate now in this Holiday season !
Three brand new missions were launched and ongoing missions orbited a planet and an asteroid and flew past a comet.
“NASA has never had the pace of so many planetary launches in such a short time,” said Green.
And three missions here were awarded ‘Best of 2011’ for innovation !
Here’s the Top NASA Planetary Science Stories of 2011 – ‘The Year of the Solar System’ – in chronological order
1. Stardust-NExT Fly By of Comet Tempel 1
Starting from the first moments of 2011 at the dawn of Jan. 1, hopes were already running high for planetary scientists and engineers busily engaged in setting up a romantic celestial date in space between a volatile icy comet and an aging, thrusting probe on Valentine’s Day.
The comet chasing Stardust-Next spacecraft successfully zoomed past Comet Tempel 1 on Feb. 14 at 10.9 km/sec (24,000 MPH) after flying over 6 Billion kilometers (3.5 Billion mi).
The craft approached within 178 km (111mi) and snapped 72 astonishingly detailed high resolution science images over barely 8 minutes. It also fulfilled the teams highest hopes by photographing the human-made crater created on Tempel 1 in 2005 by a cosmic collision with a penetrator hurled by NASA’s Deep Impact spacecraft. The probe previously flew by Comet Wild 2 in 2004 and returned cometary coma particles to Earth in 2006
Tempel 1 is the first comet to be visited by two spaceships from Earth and provided the first-ever opportunity to compare observations on two successive passages around the Sun.
Don Brownlee, the original Principal Investigator, summarized the results for Universe Today; “A great bonus of the mission was the ability to flyby two comets and take images and measurements. The wonderfully successful flyby of Comet Tempel 1 was a great cap to the 12 year mission and provided a great deal of new information to study the diversity among comets.”
“The new images of Tempel showed features that form a link between seemingly disparate surface features of the 4 comets imaged by spacecraft. Combining data on the same comet from the Deep Impact and Stardust missions has provided important new insights in to how comet surfaces evolve over time and how they release gas and dust into space”.
2. MESSENGER at Mercury
On March 18, the Mercury Surface, Space Environment, Geochemistry, and Ranging, or MESSENGER, spacecraft became the first spacecraft inserted into orbit around Mercury, the innermost planet.
So far MESSENGER has completed 1 solar day – 176 Earth days- circling above Mercury. The probe has collected a treasure trove of new data from the seven instruments onboard yielding a scientific bonanza; these include global imagery of most of the surface, measurements of the planet’s surface chemical composition, topographic evidence for significant amounts of water ice, magnetic field and interactions with the solar wind.
“MESSENGER discovered that Mercury has an enormous core, larger than Earth’s. We are trying to understand why that is and why Mercury’s density is similar to Earth’s,” Jim Green explained to Universe Today.
“The primary mission lasts 2 solar days, equivalent to 4 Mercury years.”
“NASA has granted a 1 year mission extension, for a total of 8 Mercury years. This will allow the team to understand the environment at Mercury during Solar Maximum for the first time. All prior spacecraft observations were closer to solar minimum,” said Green.
MESSENGER was launched in 2004 and the goal is to produce the first global scientific observations of Mercury and piece together the puzzle of how Mercury fits in with the origin and evolution of our solar system.
NASA’s Mariner 10 was the only previous robotic probe to explore Mercury, during three flyby’s back in the mid-1970’s early in the space age.
3. Dawn Asteroid Orbiter
The Dawn spacecraft achieved orbit around the giant asteroid Vesta in July 2011 after a four year interplanetary cruise and began transmitting the history making first ever close-up observations of the mysteriously diverse and alien world that is nothing short of a ‘Space Spectacular’.
“We do not have a good analog to Vesta anywhere else in the Solar System,” Chris Russell said to Universe Today. Russell, from UCLA, is the scientific Principal Investigator for Dawn.
Before Dawn, Vesta was just another fuzzy blob in the most powerful telescopes. Dawn has completely unveiled Vesta as a remarkably dichotomous, heavily battered and pockmarked world that’s littered with thousands of craters, mountains and landslides and ringed by mystifying grooves and troughs. It will unlock details about the elemental abundances, chemical composition and interior structure of this marvelously intriguing body.
Cataclysmic collisions eons ago excavated Vesta so it lacks a south pole. Dawn discovered that what unexpectedly remains is an enormous mountain some 16 miles (25 kilometers) high, twice the height of Mt. Everest.
Dawn is now about midway through its 1 year mission at Vesta which ends in July 2012 with a departure for Ceres, the largest asteroid. So far the framing cameras have snapped more than 10,000 never-before-seen images.
“What can be more exciting than to explore an alien world that until recently was virtually unknown!. ” Dr. Marc Rayman said to Universe Today. Rayman is Dawn’s Chief Engineer from NASA’s Jet Propulsion Lab (JPL) in Pasadena, Calif.
“Dawn is NASA at its best: ambitious, exciting, innovative, and productive.”
4. Juno Jupiter Orbiter
The solar powered Juno spacecraft was launched on Aug. 5 at Cape Canaveral Air Force Station in Florida, to embark on a five year, 2.8 billion kilometer (1.7 Billion mi) trek to Jupiter, our solar system’s largest planet. It was the first of three NASA planetary science liftoffs scheduled in 2011.
Juno’s goal is to map to the depths of the planets interior and elucidate the ingredients of Jupiter’s genesis hidden deep inside. These measurements will help answer how Jupiter’s birth and evolution applies to the formation of the other eight planets.
The 4 ton spacecraft will arrive at the gas giant in July 2016 and fire its braking rockets to go into a polar orbit and circle the planet 33 times over about one year.
The suite of nine instruments will scan the gas giant to find out more about the planets origins, interior structure and atmosphere, measure the amount of water and ammonia, observe the aurora, map the intense magnetic field and search for the existence of a solid planetary core.
“Jupiter is the Rosetta Stone of our solar system,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “It is by far the oldest planet, contains more material than all the other planets, asteroids and comets combined and carries deep inside it the story of not only the solar system but of us. Juno is going there as our emissary — to interpret what Jupiter has to say.”
5. Opportunity reaches Endeavour Crater on Mars
The long lived Opportunity rover finally arrived at the rim of the vast 14 mile (22 kilometer) wide Endeavour Crater in mid-August 2011 following an epic three year trek across treacherous dune fields – a feat once thought unimaginable. All told, Opportunity has driven more than 34 km ( 21 mi) since landing on the Red Planet way back in 2004 for a mere 90 sol mission.
In November, the rover discovered the most scientifically compelling evidence yet for the flow of liquid water on ancient Mars in the form of a water related mineral vein at a spot dubbed “Homestake” along an eroded ridge of Endeavour’s rim.
Read my story about the Homestake discovery here, along with our panoramic mosaic showing the location – created by Ken Kremer and Marco Di Lorenzo and published by Astronomy Picture of the Day (APOD) on 12 Dec. 2011.
Watch for my upcoming story detailing Opportunity’s accomplishments in 2011.
6. GRAIL Moon Mappers
The Gravity Recovery and Interior Laboratory, or GRAIL mission is comprised of twin spacecraft tasked to map the moon’s gravity and study the structure of the lunar interior from crust to core.
The dynamic duo lifted off from Cape Canaveral on September 10, 2011 atop the last Delta II rocket that will likely soar to space from Florida. After a three month voyage of more than 2.5 million miles (4 million kilometers) since blastoff, the two mirror image GRAIL spacecraft dubbed Grail-A and GRAIL-B are sailing on a trajectory placing them on a course over the Moon’s south pole on New Year’s weekend.
Each spacecraft will fire the braking rockets for about 40 minutes for insertion into Lunar Orbit about 25 hours apart on New Year’s Eve and New Year’s Day.
Engineers will then gradually lower the satellites to a near-polar near-circular orbital altitude of about 34 miles (55 kilometers).
The spacecraft will fly in tandem and the 82 day science phase will begin in March 2012.
“GRAIL is a Journey to the Center of the Moon”, says Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology (MIT). “GRAIL will rewrite the book on the formation of the moon and the beginning of us.”
“By globally mapping the moon’s gravity field to high precision scientists can deduce information about the interior structure, density and composition of the lunar interior. We’ll evaluate whether there even is a solid or liquid core or a mixture and advance the understanding of the thermal evolution of the moon and the solar system,” explained co-investigator Sami Asmar to Universe Today. Asmar is from NASA’s Jet Propulsion Laboratory (JPL)
7. Curiosity Mars Rover
The Curiosity Mars Science Lab (MSL) rover soared skywards on Nov. 26, the last of 2011’s three planetary science missions. Curiosity is the newest, largest and most technologically sophisticated robotic surveyor that NASA has ever assembled.
“MSL packs the most bang for the buck yet sent to Mars.” John Grotzinger, the Mars Science Laboratory Project Scientist of the California Institute of Technology, told Universe Today.
The three meter long robot is the first astrobiology mission since the Viking landers in the 1970’s and specifically tasked to hunt for the ‘Ingredients of Life’ on Mars – the most Earth-like planet in our Solar System.
Video caption: Action packed animation depicts sequences of Curiosity departing Earth, the nail biting terror of the never before used entry, descent and landing on the Martian surface and then looking for signs of life at Gale Crater during her minimum two year expedition across hitherto unseen and unexplored Martian landscapes, mountains and craters. Credit: NASA
Curiosity will gather and analyze samples of Martian dirt in pursuit of the tell-tale signatures of life in the form of organic molecules – the carbon based building blocks of life as we know it.
NASA is targeting Curiosity to a pinpoint touch down inside the 154 km (96 mile) wide Gale Crater on Aug. 6, 2012. The crater exhibits exposures of phyllosilicates and other minerals that may have preserved evidence of ancient or extant Martian life and is dominated by a towering 3 mile (5 km) high mountain.
“10 science instruments are all aimed at a mountain whose stratigraphic layering records the major breakpoints in the history of Mars’ environments over likely hundreds of millions of years, including those that may have been habitable for life,” Grotzinger told me.
This past year Ken was incredibly fortunate to witness the ongoing efforts of many of these magnificent endeavors.
Thirty-five years after NASA’s Mariner 10 interplanetary probe flew by and imaged less than half of tiny Mercury’s surface, NASA’s MESSENGER spacecraft now orbits our Solar System’s enigmatic and poorly understood innermost planet. After a six-and-a-half-year journey — which included three flybys of Mercury — MESSENGER is now the first spacecraft to take up long-term residence around this hard-to-reach and hellish planet.
Crater-scarred Mercury lies at an average distance of only 58 million kms from the Sun, so searingly close that its angular separation (or elongation) from our own star is never more than 28 degrees. This all makes it extremely difficult to study from Earth.
To get some perspective on the findings and Mercury itself, we turned to the MESSENGER Project Scientist Ralph McNutt at Johns Hopkins University’s Applied Physics Lab.
Dorminey — Is the MESSENGER data already shaking up Mercury paradigms?
McNutt — Yes – the biggest issue has been the volatile content which is likely going to lead to an interesting, but productive debate, about implications for planetary origins in the inner solar system.
“Volatile” elements are those with relatively low melting and boiling points. “Refractory” elements have relatively high boiling and melting points. If Mercury has a large core due to the surface being “boiled off” by a hot solar wind or hotter Sun in the early days of the solar system, or by a giant impact, then it is more difficult – but perhaps not impossible – for the volatile to refractory ratio, as exemplified by the potassium to thorium ratio (K/Th), to be as high on Mercury as at Earth, Mars, and Venus. And yet that is what the data are saying.
Dorminey — What could explain Mercury’s magnetic field being offset north of the planet’s center by 20 percent of its radius? Was this offset due to a giant impactor?
McNutt — My guess would be that the offset is not due to a giant impactor. But we still do not have a good explanation.
Dorminey — But does the in situ measurement of this magnetic field also confirm that Mercury still has an active magnetic dynamo?
McNutt — There seems to be no way that [Mercury] can escape having a dynamo, so that already makes for implications about Mercury’s cooling history and the chemical mixture [needed] for the dynamo action. There needs to be mostly iron, but something else must be mixed in to help lower the freezing point, otherwise the dynamo should have frozen out some time back.
“Dynamo” in either a planetary or commercial context refers to the generation of electricity by movement of a conductor with respect to a preexisting magnetic filed. Such a movement produces an electrical current, which, in turn, produces a magnetic field.
In a planet, the conductor is a liquid with motion derived from the rotational energy of the planet. But a full theoretical description of how planetary dynamos work is still lacking and is the subject of ongoing research.
Dorminey — A popular formation theory, which would explain its anomalously large iron core, is that early Mercury was stripped of its outer layers following a giant impact. Do you adhere to this idea?
McNutt — Nominally, a high volatile content – expressed via a high potassium to thorium ratio (K/Th), which we have measured with the MESSENGER gamma-ray spectrometer, would rule against such a massive impact. The thinking has been that the volatile content would not re-accrete and so one would be left with a low global average such as is measured for the Moon. We will see – I do not think the verdict is in yet on this one.
Dorminey — What is the significance of and where did it get its surface sulfur and potassium?
McNutt — Sulfur and potassium were both elements in the initial solar nebula. The real question is what led to their placement and relative concentrations on the surface of Mercury.
Dorminey — What’s the significance of the MESSENGER-imaged volcanic vents? Is Mercury still tectonically active?
McNutt — The volcanic vents tells us that volcanism was a significant part of the geologic history of the planet. The planet has cooled a lot since there was a lot of activity and continues to cool. The level of activity is likely low at best – but if we see an active [volcanic] vent, we will definitely let the world know.
Dorminey — We know that Mercury has an exosphere, but could Mercury ever have had anything approaching an Earthlike atmosphere?
McNutt — Any sort of a stable Earth-like atmosphere is not in the cards. Mercury is too small with too small a gravity field to hold on to anything for a long time. If there was sufficiently rapid outgassing , then one could have built up an atmosphere of something that might have Earth-like pressures, but certainly no oxygen, and not for long given the temperature.
Dorminey — What is still the most puzzling to you about Mercury?
McNutt — Right now, the biggest puzzle is how to put together the magnetic field configuration (with the offset), with a dynamo, and the topography and gravity data all in a self-consistent description of the planet. There will be some more papers coming out on these topics in the near future.
Dorminey — If money were no object, what would be the ultimate science exploration strategy for Mercury? Are there any plans in the works for a lander?
McNutt — To really understand the solar system, we need to put together a coherent chronology of formation and early thermal evolution of the planets and other solar system objects. To do that “right” one needs well-characterized samples returned from the surface or drilled from the near-surface, in pristine environments and delivered to labs on Earth. Sample returns are hard – but not as hard as placing such equipment in situ. Following the next level of intense study by BepiColombo (the ESA orbital mission now in development), the next step is a lander. There are no plans for such a mission at present. An interesting question is which is harder: a sample return mission from Mercury or from Venus.
Dorminey — With dayside temperatures of 630 kelvin and nightside temperatures of 95 kelvin, could Mercury have ever been a candidate for liquid water or oceans?
McNutt — No.
Dorminey — Could Mercury have ever had microbial life?
McNutt — Before it was known that Mercury rotated, there was some speculation that there might be a zone of perpetual twilight between the Sun-facing hot side and the Sun-shadowed cold side a “twilight zone” where something [like microbial life] might be possible. In actuality, the region between hot and cold would have been fairly abrupt (depending on the thermal conductivity of the rocks). As Mercury does rotate, no such region exists.
Dorminey — What’s the ultimate significance of planetary science’s study of Mercury? Does it offer a template for what you expect in other solar systems, or does your gut tell you that it’s a total fluke?
McNutt — Knowing more about Mercury, and Venus and Mars tells us about the “terrestrial planets” as a whole and what was common – and special – about ours – and their origins. While the new exoplanet discoveries are extremely interesting, we will not get as close to those planets as we can get to the ones in our own Solar System anytime soon. We have yet to be able to resolve other “Mercurys” in our exoplanet searches, so it is as likely as good a template as any. In learned circles at one time in the not too distant past, the entire solar system was considered to be a total fluke.
A trio of NASA’s Planetary Science mission’s – Mars Science Laboratory (MSL), Dawn and MESSENGER – has been honored by Popular Science magazine and selected as ‘Best of What’s New’ in innovation in 2011 in the aviation and space category.
The Curiosity Mars Science Laboratory was just launched to the Red Planet on Saturday, Nov. 26 and will search for signs of life while traversing around layered terrain at Gale Crater. Dawn just arrived in orbit around Asteroid Vesta in July 2011. MESSENGER achieved orbit around Planet Mercury in March 2011.
Several of the top mission scientists and engineers provided exclusive comments about the Popular Science recognitions to Universe Today – below.
“Of course we are all very pleased by this selection,” Prof. Chris Russell, Dawn Principal Investigator, of UCLA, told Universe Today.
Dawn is the first mission ever to specifically investigate the main Asteroid Belt between Mars and Jupiter and will orbit both Vesta and Ceres – a feat enabled solely thanks to the revolutionary ion propulsion system.
“At the same time I must admit we are also not humble about it. Dawn is truly an amazing mission. A low cost mission, using NASA’s advanced technology to enormous scientific advantage. It is really, really a great mission,” Russell told me.
Vesta is the second most massive asteroid and Dawn’s discoveries of a surprisingly dichotomous and battered world has vastly exceeded the team’s expectations.
“Dawn is NASA at its best: ambitious, exciting, innovative, and productive,” Dr. Marc Rayman, Dawn’s Chief Engineer from the Jet Propulsion Lab (JPL), Pasadena, Calif., told Universe Today.
“This interplanetary spaceship is exploring uncharted worlds. I’m delighted Popular Science recognizes what a marvelous undertaking this is.”
JPL manages both Dawn and Mars Science Laboratory for NASA’s Science Mission Directorate in Washington, D.C.
Dawn is an international science mission. The partners include the German Aerospace Center (DLR), the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute.
“Very cool!”, John Grotzinger, the Mars Science Laboratory Project Scientist of the California Institute of Technology, told Universe Today.
“MSL packs the most bang for the buck yet sent to Mars.”
Curiosity is using an unprecedented precision landing system to touch down inside the 154 km (96 miile) wide Gale Crater on Aug. 6, 2012. The crater exhibits exposures of phyllosilicates and other minerals that may have preserved evidence of ancient or extant Martian life and is dominated by a towering mountain.
“10 instruments all aimed at a mountain higher than any in the lower 48 states, whose stratigraphic layering records the major breakpoints in the history of Mars’ environments over likely hundreds of millions of years, including those that may have been habitable for life.”
“It’s like a trip down the Grand Canyon 150 years ago, with the same sense of adventure, but with a lot of high tech equipment,” Grotzinger told me.
MSL also has an international team of over 250 science investigators and instruments spread across the US, Europe and Russia.
MESSENGER is the first probe to orbit Mercury and the one year primary mission was recently extended by NASA.
Sean Solomon, of the Carnegie Institution of Washington, leads the MESSENGER mission as principal investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft for NASA.
“Planetary has 3 missions there… Dawn, MESSENGER, and MSL,” Jim Green proudly said to Universe Today regarding the Popular Science magazine awards. Green is the director, Planetary Science Division, NASA Headquarters, Washington
“Three out of 10 [awards] is a tremendous recognition of the fact that each one of our planetary missions goes to a different environment and takes on new and unique measurements providing us new discoveries and constantly changes how we view nature, ourselves, and our place in the universe.”
Read more about the Popular Science citations and awards here
Read continuing features about Curiosity, Dawn and MESSENGER by Ken Kremer starting here:
How long has it been since you’ve taken a good look at Mercury? For the backyard astronomer, all we’ll ever see is the speedy little planet as a bright crescent a few times a year. But, for the MESSENGER spacecraft, Mercury isn’t quite as boring as you might think! Some strange new features have been spotted and a planetary geologist speculates they could be attributed to hydrogen venting from the planet’s interior.
While it’s only been a week since MESSENGER sent back some curious photos of Mercury’s surface, the revelation has created quite a stir in the planetary science community. These observations have included evidence of shallow depressions which have formed into non-uniform crater structures which appear to be recent. In addition, they have a high albedo – indicative of some sort of reflective material. But, what?
According to Marvin Herndon, an independent scientist based in San Diego, Mercury formed under great pressure and high temperature – enough to leave iron in a molten state. If so, it should be responsible for absorbing large amounts of hydrogen. As it cools and transforms to a solid state, the hydrogen is then released, forming a type of “geyser” on the planet’s surface.
“These hydrogen geysers could certainly have caused the rimless depressions that MESSENGER sees.” says Herndon, a self-proclaimed maverick in the world of planetary geology.
As the hydrogen is released from below the planet’s surface, it would also react with other elements it would encounter – possibly iron sulphide, commonly found on Mercury’s surface. This would cause a reduction to metallic iron. From there it would form a light “dust” which could account for the bright, new features seen by MESSENGER.