Mars! Martian meteorites make their way to Earth after being ejected from Mars by a meteor impact on the Red Planet. Image: NASA/National Space Science Data Center.
Sometimes, the best way to study Mars is to stay home. There’s no substitute for actual missions to Mars, but pieces of Mars have made the journey to Earth, and saved us the trip. Case in point: the treasure trove of Martian meteorites that NASA is gathering from Antarctica.
NASA scientists aren’t the first ones to find meteorites in the Earth’s polar regions. As early as the 9th century, people in the northern polar regions made use of iron from meteorites for tools and hunting weapons. The meteorite iron was traded from group to group over long distances. But for NASA, the hunt for meteorites is focused on Antarctica.
In Antarctica, the frigid temperatures preserve meteorites for a long time, which makes them valuable artifacts in the quest to understand Mars. Meteorites tend to accumulate in places where creeping glacial ice moves them to. When the ice meets a rock obstacle, the meteorites are deposited there, making them easier to find. Recently arrived meteorites are also easily spotted on the surface of the Antarctica ice.
The US began collecting meteorites in Antarctica in 1976, and to date more than 21,000 meteorites and meteorite fragments have been found. In fact, more of them are found in Antarctica than in the rest of the world combined. These meteorites are then shared with scientists around the world.
Collecting meteorites in Antarctica is not a walk in the park. It’s physically gruelling and hazardous work. Antarctica is not an easy environment to live and work in, and just surviving there takes planning and teamwork. But the scientific payoff is huge, which keeps NASA going back.
Meteorites from the Moon and other bodies also arrive on Earth, and are collected in Antarctica. They can tell scientists important things about the evolution and formation of the Solar System, the origin of organic chemical compounds necessary for life, and the origin of the planets themselves.
How Do Martian Meteorites Get To Earth?
A few things have to go right for a Martian meteorite to make it to Earth. First, a meteorite has to collide with Mars. That meteorite has to be big enough, and hit the surface of Mars with enough force, that rock from Mars is propelled off the surface with enough speed to escape Mars’ gravity.
After that, the meteor has to travel through space and avoid a thousand other fates, like being drawn to one of the other planets, or the Sun, by the gravitational pull of those bodies. Or being flung off into the far reaches of empty space, lost forever. Then, if it manages to make it to Earth, and be pulled in by Earthly gravity, it must be large enough to survive entry into Earth’s atmosphere.
The Science
Part of the scientific value in meteorites lies not in their source, but in the time that they were formed. Some meteorites have travelled through space for so long, they’re like time travellers. These ancient meteorites can tell scientists a lot about conditions in the early Solar System.
This the Hoba meteorite from Namibia. At 60 tonnes, it is the largest known intact meteorite. Image: Patrick Giraud, http://creativecommons.org/licenses/by/2.5
Meteorites from Mars tell scientists a few things. Since they’ve survived re-entry into Earth’s atmosphere, they can tell engineers about the dynamics of such a journey, and help inform spacecraft design. Since they contain chemical signatures and elements unique to Mars, they can also tell mission specialists things about surviving on Mars.
They can also provide clues to one of the greatest mysteries in space exploration: Did life exist on Mars? A Martian meteorite found in the Sahara desert in 2011 contained ten times the amount of water as other Martian meteorites, and added evidence to the idea that Mars was once a wet world, suitable for life.
NASA’s program to hunt for meteorites in Antarctica has been going strong for many years, and there’s really no reason to stop doing it, since this is the only way to get Martian samples into a laboratory. Each one they find is like a puzzle piece, and like a jigsaw puzzle, you never know which one will complete the big picture.
The Wow! signal recorded on August 15, 1977. The ones, twos and threes indicate weak background noise. Letters, especially those closer to the end of the alphabet, represent stronger signals. The “6EQUJ5” is read from top to bottom (see graph below) and shows the signal rising from “6” to “U” before dropping back down to “5”. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)
The Wow! signal recorded on August 15, 1977. The ones, twos and threes indicate weak background noise. Letters, especially those closer to the end of the alphabet, represent stronger signals. The “6EQUJ5” is read from top to bottom (see graph below) and shows the signal rising from “6” to “U” before dropping back down to “5”. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)
Comets get blamed for everything. Pestilence in medieval Europe? Comets! Mass extinctions? Comets! Even the anomalous brightness variations in the Kepler star KIC 8462852 was blamed for a time on comets. Now it looks like the most famous maybe-ET signal ever sifted from the sky, the so-called “Wow!” signal, may also be traced to comets.
Say it ain’t so!
The Big Ear Observatory, on the grounds of Ohio Wesleyan University, operated from 1963-1998. It was part of Ohio State University’s long-running Search for Extraterrestrial (SETI) program. The observatory was torn down in 1998 to make room for a golf course. Credit: Bigear.org / NAAPO
In August 1977, radio astronomer Jerry Ehman was looking through observation data from the Ohio State’s now-defunct Big Ear radio telescope gathered a few days earlier on August 15. He was searching for signals that stood apart from the background noise that might be broadcast by an alien civilization. Since hydrogen is the most common element in the universe and emits energy at the specific frequency of 1420 megahertz (just above the TV and cellphone bands), aliens might adopt it as the “lingua franca” of the cosmos. Scientists here on Earth concentrated radio searches at and around that frequency looking for strong signals that mimicked hydrogen.
Ehman’s searches turned up mostly background noise, but that mid-August night he spotted a surprise — a vertical column with the alphanumerical sequence “6EQUJ5″ that indicated a strong signal at hydrogen’s frequency. Exactly as predicted. Big Ear picked up the signal from near the 5th magnitude star Chi-1 Sagittarii in eastern Sagittarius not far from the globular cluster M55.
Astonished by the find, Ehman pulled out a red pen, circled the sequence and wrote a big “Wow!” in the margin. Ever since, it’s been called the Wow! signal and considered one of the few signals from space that defies explanation. Before we look at how that may change, let’s make sense of the code.
Plot of signal strength vs time of the Wow! signal on August 15, 1977. The signal rose and fell during the 72 seconds observation window. Credit: Maksim Rossomakhin
Each digit on the chart corresponded to a signal intensity from 0 to 35. Anything over “9” was represented by a letter from A to Z. It was probably the “U” that knocked Ehman’s socks off, since it indicated to a radio burst 30 times greater than the background noise of space.
In Big Ear’s 35 years of operation, it was the most intense, unexplainable signal ever recorded. What’s more, it was narrowly focused and very close to hydrogen’s special frequency.
Big Ear listened for just 72 seconds before Earth’s rotation carried the signal’s location out of “view” of antenna. Since the radio array had two feed horns, the transmission was expected to appear three minutes apart in each of the horns, but only a single one ever picked it up.
Despite follow-up observations byEhman and others (more than 100 studies were made of the region) the signal was gone. Never heard from again. Nor has anything else like it ever been recorded anywhere else in the sky.
Careful scrutiny eliminated earthbound possibilities such as aircraft or satellites. Nor would anyone have been transmitting at 1420 MHz since it was within a protected part of the radio spectrum used by astronomers and off-limits to regular broadcasters. The nature of the signal implied a point source somewhere beyond the Earth. But where?
On August 15, 1977, periodic comets 266P/Christensen and 335P/Gibbs would have both been very close to the narrow swath of sky south of Chi Sagittarii where the Wow! signal was received. Could they be implicated? Diagram: Bob King, source: Stellarium
If it really was an attempt at alien contact, why try only once and for so short a time interval? Even Ehman doubted (and still doubts) an extraterrestrial intelligence origin, but a much more recent suggestion made by Prof. Antonio Paris of St. Petersburg College, Florida may offer an answer. Paris earlier worked as an analyst for the U.S. Department of Defense and returned to the “scene of the crime” looking for any likely suspects. After studying astronomical databases, he discovered that two faint comets, 266P/Christensen and 335P/Gibbs, discovered only within the past decade, had been plying the very area of the Wow! signal on August 15, 1977.
A huge cloud of hydrogen surrounded Comet Hale-Bopp when it neared the Sun in 1997. Ultraviolet light, charted by the SWAN instrument on the SOHO spacecraft, revealed that the cloud far exceeded the great comet’s visible tail (inset photo) — 70 times wider than the Sun itself (yellow circle to scale at right). Credit: SOHO (ESA & NASA) and SWAN Consortium / inset: Dennis di Cicco
If you recall, a comet has two or three basic parts: a fuzzy head or coma and one or two tails streaming off behind. Invisible to earthbound telescopes, but showing clearly in orbiting telescopes able to peer into ultraviolet light, the coma is further wrapped in a huge cloud of neutral hydrogen gas.
As the Sun warms a comet’s surface, water ice or H2O vaporizes from its nucleus. Energetic solar UV light breaks down those water molecules into H2 and O. The H2 forms a huge, distended halo that can expand to many times the size of the Sun.
Paris published a paper earlier this year exploring the possibility that the hydrogen envelopes of either or both comets were responsible for the strong 1420 MHz signal snagged by Big Ear. On the surface, this makes sense, but not all astronomers agree. First off, if comets are so radio-bright in hydrogen light, why don’t radio telescopes pick them up more often? They don’t. Second, some astronomers doubt that the signals from these comets would have been strong enough to be picked up by the array.
Image of the full page of the computer printout that contains the “Wow!” signal. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)
A quick check on 266P and 335P at the time of the signal show them both around 5 a.u. from the sun (Jupiter’s distance) and extremely faint at magnitudes 22 and 27 respectively. Were they even active enough at those distances to form clouds big enough for the antenna to detect?
Paris knows there’s only one way to find out. Comet 266P/Christensen will swing through the same area again on Jan. 25, 2017, while 335P/Gibbs follows suit on January 7, 2018. Unable to use an existing radio telescope (they’re all booked up!), he’s begun a gofundme campaign to purchase and install a 3-meter radio telescope to track and analyze the spectra of these two comets. The goal is $20,000 and Paris is already well on his way there.
It would be a little bit sad if the Wow! signal turned out to be a “just a comet”, but the possibility of solving a 39-year-old mystery would ultimately be more satisfying, don’t you think?
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity's first interstellar voyage. Credit: breakthroughinitiatives.org
For generations, human beings have fantasized about the possibility of finding extra-terrestrial life. And with our ongoing research efforts to discover new and exciting extrasolar planets (aka. exoplanets) in distant star systems, the possibility of actually visiting one of these worlds has received a real shot in the arm. Unfortunately, given the astronomical distances involved, not to mention the cost of mounting an expedition, doing so presents numerous significant challenges.
However, Russian billionaire Yuri Milner and the Breakthrough Foundation – an international organization committed to exploration and scientific research – is determined to mount an interstellar mission to Alpha Centauri, our closest stellar neighbor, in the coming years. With the backing of such big name sponsors as Mark Zuckerberg and Stephen Hawking, his latest initiative (named “Project Starshot“) aims to send a tiny spacecraft to the Alpha Centauri system to search for planets and signs of life.
The Solar and Heliospheric Observatory (SOHO) took these photos of Mercury during its last transit of the Sun on Nov. 8, 2006. Credit: NASA/ESA
Be sure to mark your calendar for May 9. On that day, the Solar System’s most elusive planet will pass directly in front of the Sun. The special event, called a transit, happens infrequently. The last Mercury transit occurred more than 10 years ago, so many of us can’t wait for this next. Remember how cool it was to see Venus transit the Sun in 2008 and again in 2012? The views will be similar with one big difference: Mercury’s a lot smaller and farther away than Venus, so you’ll need a telescope. Not a big scope, but something that magnifies at least 30x. Mercury will span just 10 arc seconds, making it only a sixth as big as Venus.
Two basic types of safe solar filters for telescopes: an aluminized polymer such as Baader film and a dedicated glass solar filter for a particular make and model. Credit: Bob King
Map showing Mercury’s path across the Sun at three key points on May 9: transit start or ingress (left); midpoint and transit end or egress (right). Credit: Tom Ruen with additions by author
If I might make a suggestion, consider buying a sheet of Baader AstroSolar aluminized polyester film and cutting it to size to make your own filter. Although the film’s crinkly texture might make you think it’s flimsy or of poor optical quality, don’t be deceived by appearances.
The material yields both excellent contrast and a pleasing neutral-colored solar image. You can purchase any of several different-sized films to suit your needs either from Astro-Physicsor on Amazon.com. Prices range from $40-90.
Nov. 8, 2006 Transit of Mercury by Dave Kodama
With filter material in hand, just follow these instructions to make your own, snug-fitting telescopic solar filter. Even I can do it, and I kid you not that I’m a total klutz when it comes to building things. If for whatever reason you can’t get a filter, go to Plan B. Put a low power eyepiece in your scope and project an image of the Sun onto a sheet of white paper a foot or two behind the eyepiece.
World map showing where the May 9-10 Mercury transit will be visible. Universal times of the four key contacts (see below for details), mid-transit time and position angle on the Sun’s limb where the planet will first appear and disappear are given at upper left. Credit: Xavier M. Jubier
Since May 9th is a Monday, I’ve a hunch a few of you will be taking the day off. If you can’t, pack a telescope and set it up during lunch hour to share the view with your colleagues. Mercury will spend a leisurely 7 1/2 hours slowly crawling across the Sun’s face, traveling from east to west. The entire transit will be visible across the eastern half of the U.S., most of South America, eastern and central Canada, western Africa and much of western Europe. For the western U.S., Alaska and Hawaii the Sun will rise with the transit already in progress.
Time Zone
Eastern (EDT)
Central (CDT)
Mountain (MDT)
Pacific (PDT)
Transit start
7:12 a.m.
6:12 a.m.
5:12 a.m.
Not visible
Mid-transit
10:57 a.m.
9:57 a.m.
8:57 a.m.
7:57 a.m.
Transit end
2:42 p.m.
1:42 p.m.
12:42 p.m.
11:42 a.m.
Nov. 2006 animation by Hinode. Credit: NASA
At first glance, the planet might look like a small sunspot, but if you look closely, you’ll see it’s a small, perfectly circular black dot compared to the out-of-round sunspots which also possess the classic two-part umbra-penumbra structure. Oh yes, it also moves. Slowly to be sure, but much faster than a typical sunspot which takes nearly two weeks to cross the Sun’s face. With a little luck, a few sunspots will be in view during transit time; compared to midnight Mercury their “black” umbral cores will look deep brown.
I want to alert you to four key times to have your eye glued to the telescope; all occur during the 3 minutes and 12 seconds when Mercury enters and exits the Sun. They’re listed below in Universal Time or UT. To convert UT to EDT, subtract 4 hours; CDT 5 hours; MDT 6 hours, PDT 7 hours, AKDT 8 hours and HST 10 hours.
The black drop effect seen to good advantage during the June 2004 transit of Venus. Credit: Jan Herold
First contact (11:12 UT): Watch for the first hint of Mercury’s globe biting into the Sun just south of the due east point on along the edge of disk’s edge. It’s always a thrill to see an astronomical event forecast years ago happen at precisely the predicted time.
Second contact (11:15 UT): Three minutes and 12 seconds later, the planet’s trailing edge touches the inner limb of the Sun at second contact. Does the planet separate cleanly from the solar limb or briefly remain “connected” by a narrow, black “line”, giving the silhouette a drop-shaped appearance?
This “black drop effect”is caused primarily by diffraction, the bending and interfering of light waves when they pass through the narrow gap between Mercury and the Sun’s edge. You can replicate the effect by bringing your thumb and index finger closer and closer together against a bright backdrop. Immediately before they touch, a black arc will fill the gap between them.
The “black drop effect” can be reproduced by slowly bringing your thumb and index finger together. It’s caused by diffraction combined with blurring from the atmosphere. Credit: Bob King
Third contact (18:39 UT): A minute or less before Mercury’s leading edge touches the opposite limb of the Sun at third contact, watch for the black drop effect to return.
Fourth contact (18:42 UT): The moment the last silhouetted speck of Mercury exits the Sun. Don’t forget to mark your calendar for November 11, 2019, date of the next transit, which also favors observers in the Americas and Europe. After that one, the next won’t happen till 2032.
Other interesting visuals to keep an eye out for is a bright ring or aureole that sometimes appears around the planet caused when our brain exaggerates the contrast of an object against a backdrop of a different brightness. Another spurious optical-brain effect keen-eyed observers can watch for is a central bright spot inside Mercury’s black disk. Use high power to get the best views of these obscure but fascinating phenomena seen by many observers during Mercury transits.
NASA’s Hinode X-ray telescope captured this view of Mercury silhouetted against the Sun’s corona during the Nov. 2006 transit. Similar views are possible in H-alpha light should the planet pass in front of a prominence. Credit: NASA
While I’ve been talking all “white light” observation, the proliferation of relatively inexpensive and portable hydrogen-alpha telescopes in recent years makes them another viewing option with intriguing possibilities. These instruments show solar phenomena beyond the Sun’s limb, including the flaming prominences normally seen only during a total eclipse. That makes it possible to glimpse Mercury minutes in advance of the transit (or minutes after transit end) silhouetted against a prominence or nudging into the rim furry ring of spicules surrounding the outer limb. Wow!
One final note. Be careful never to look directly at the Sun even for a moment during the transit. Keep your eyes safe! When aiming a telescope, the safest and easiest way to center the Sun in the field of view is to shift the scope up and down and back and forth until the shadow the tube casts on the ground is shortest. Try it.
I hope the weather gods smile on you on May 9, but it they don’t or if you live where the transit won’t be visible, Italian astrophysicist Gianluca Masi will stream it live on his Virtual Telescope websitestarting at 11:00 UT (6 a.m CDT).
Here on Earth, we’re always concerned with the weather.
“OK Google, am I going to need an umbrella tomorrow?”
[Google] No, rain is not expected tomorrow in Curtney. The forecast is 20 degrees and partly cloudy.
Uh, it’s pronounced “Courtenay”.
Fine, what if I lived on the Moon? OK Google, am I going to need an umbrella tomorrow on the Moon?
[Google] …
Let’s take Google’s silence for uncertainty.
The names of geological features on the Moon sure evoke mental images of weather. There’s the Ocean of Storms, also known as Oceanus Procellarum, or the Ocean of Clouds – aka Mare Nubium. In fact, most of the regions of the Moon are named after oceans. That’s got to count for something, right?
Many of the features of the moon were thought to be oceans. Credit: NASA
They got these names because the early astronomers thought they were seeing actual oceans on the Moon. They imagined vast seas, where heroic 6-legged creepy bug people plied the icy waves seeking fame, fortune and lunar plunder. I don’t know, like gold cheese or something. Seriously, they were making a lot of this stuff up until telescopes were invented.
But when the NASA astronauts finally set foot on the Moon, they knew they wouldn’t need to pack their snorkeling gear because there weren’t any oceans on the Moon, or really any atmosphere. The Moon is almost as dead and lifeless as space itself.
The storms we see battering the astronauts on every Mars science fiction story just can’t happen on the Moon because there’s no air there.
There’s an ongoing lethal radiation solar wind blowing from the Sun and deep space, but nothing that you’d be able to windsurf too.
So why isn’t there an atmosphere on the Moon? It all comes down to gravity. The Moon has about 1% of the mass of the Earth, which means that it doesn’t have enough gravity to hold onto any gas atmosphere. Anything that it did have would have been blown away by the solar wind billions of years ago.
We did a whole episode on what it would take to terraform the Moon, and it turns out you’d need to constantly replenish the atmosphere.
In fact, this is one of the reasons why the Martian atmosphere is so thin. It was probably thicker in the past, but the solar winds stripped off all the lighter atmosphere long ago. Now it’s just 1% the thickness of the Earth’s atmosphere.
Now, I’ve said that the Moon has almost no atmosphere. But almost no means partly yes. There is in fact an incredibly thin atmosphere surrounding the Moon which measures about a hundred trillionth the thickness of the Earth’s atmosphere.
There are a few sources of this atmosphere. First there’s volcanic outgassing that comes from the Moon. this contributes a little helium and radon. Then there’s the constant micrometeorite bombardment that kicks up pulverized lunar regolith.
Lunar sunrise sketches drawn by Commander E. A. Cernan during the Apollo 17 mission. Credit: NASA
But perhaps the strangest atmospheric feature is a storm that does rage across the surface of the Moon right at the terminator, the exact line between the Moon’s day side and its night side. It turns out the day side of the Moon is positively charged, and the night side is negatively charged.
As the terminator moves, the polarity of the dust flips and it drives it sideways. In fact, the astronauts who walked on the Moon actually reported seeing this. They saw bands or twilight rays in the sky around lunar sunrise/sunset.
Without a thick atmosphere, the surface of the Moon just doesn’t have any appreciable weather and definitely doesn’t have storms like we have on Earth. Mark Watney will need some other reason than weather to be stuck behind on the Moon.
Artist's impression of a Near-Earth Asteroid passing by Earth. Credit: ESA
Of the more than 600,000 known asteroids in our Solar System, almost 10 000 are known as Near-Earth Objects (NEOs). These are asteroids or comets whose orbits bring them close to Earth’s, and which could potentially collide with us at some point in the future. As such, monitoring these objects is a vital part of NASA’s ongoing efforts in space. One such mission is NASA’s Near-Earth Object Wide-field Survey Explorer (NEOWISE), which has been active since December 2013.
And now, after two years of study, the information gathered by the mission is being released to the public. This included, most recently, NEOWISE’s second year of survey data, which accounted for 72 previously unknown objects that orbit near to our planet. Of these, eight were classified as potentially hazardous asteroids (PHAs), based on their size and how closely their orbits approach Earth.
The waxing gibbous Moon passes Mercury (low to the right). Image credit and copyright: Tavi Greiner
Have you ever seen Mercury? The diminutive innermost world takes the center stage next month, as it transits the Sun as seen from our early perspective on May 9th. This week, we’d like to turn your attention to bashful Mercury’s dusk apparition, which sets up the clockwork celestial gears for this event. Continue reading “Prelude to Transit: Catching Mercury Under Dusk Skies”
The Wild Duck Cluster photographed on amateur astrophotography equipment. Credit: Creative Commons/Rawastrodata
Welcome back to another edition of Messier Monday! Today, we continue in our tribute to Tammy Plotner with a look at the M11 Wild Duck Cluster!
In the 18th century, French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky while searching for comets. Hoping to ensure that other astronomers did not make the same mistake, he began compiling a list of 1oo of them. This list came to be known as the Messier Catalog, and would have far-reaching consequences.
One of these objects is M11, otherwise known as The Wild Duck Cluster, an open cluster located in the constellation Scutum, near the northern edge of a rich Milky Way star cloud (the Scutum Cloud). This open star cluster is one of the richest and most compact of all those known, composed of a few thousand hot, young stars that are only a few million years old.
Massive sunspot AR 2529 at sunset. Image credit and copyright: Gadi Eidelheit.
Our seemly placid host star is just full of surprises.
Just one week ago, it looked like we were set to enter the first spotless stretch of 2016, as the Earthward face of Sol presented one lonely sunspot group going ’round the limb, headed towards the solar far side. Continue reading “Huge Sunspot Turns Earthward”
A black hole is the final form a massive star collapses to. The light (and spacetime itself) is warped around the black hole's event horizon due to extreme gravitational effects. This is as accurate as we can be to visualizing an actual black hole as it was generated with a code that implemented General Relativity accurately. Credit and Copyright: Paramount Pictures/Warner Bros.
Mathematical Model used to create the image developed by Dr. Kip Thorne
A neutron star is perhaps one of the most awe-inspiring and mysterious things in the Universe. Composed almost entirely of neutrons with no net electrical charge, they are the final phase in the life-cycle of a giant star, born of the fiery explosions known as supernovae. They are also the densest known objects in the universe, a fact which often results in them becoming a black hole if they undergo a change in mass.
For some time, astronomers have been confounded by this process, never knowing where or when a neutron star might make this final transformation. But thanks to a recent study by a team of researchers from Goethe University in Frankfurt, Germany, it may now be possible to determine the absolute maximum mass that is required for a neutron star to collapse, giving birth to a new black hole.
