Tag Archives: Mars

Climate Change in the Solar System

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We are all familiar with the climate on Earth: the seasons, the range of surface temperatures that are just right for being a water world, the oxygen we breathe, the ozone layer that protects us from UV radiation. In short: habitable.

So what other bodies in the Solar System might be (or might have been) habitable, and why aren’t they today?

Mars probably comes to mind, and for good reason. Mars has the most similar climate to our own, with water ice caps at the poles, seasonal snow, and dust storms. This is because Mars has a similar axial tilt as the Earth, which creates similar seasonal temperature variations. However, the colder average temperatures and the thin atmosphere mean liquid water can only exist on the surface around midsummer and at the lowest elevations (where the atmospheric pressure is greatest). The thin atmosphere also means the surface is exposed to intense UV radiation. Mars may not be habitable today (for life on the surface), but climates change.

 

Mars

Hubble image of Mars engulfed in a global dust storm, with its polar caps peeking through. Image courtesy of NASA.

Several lines of evidence point to Mars being wet and warm early in its history. Water-carved channels, minerals formed by interaction with groundwater (like gypsum), river delta deposits, and what may be a shoreline all the way around the northern lowlands (which would have been a giant ocean) all point to lots of liquid water on the surface sometime in the distant past.

So why was Mars so much warmer and wetter than it is today, and why did it change? These are fundamental questions about climate change that have yet to be fully answered.

Early Mars likely had a thicker atmosphere, made of mostly CO2 like it is today, which would have warmed the surface through the greenhouse effect. One way to understand the climate early in Mars history is to study the oldest rocks and landforms. Another is to look at more recent climate changes, which are likely preserved in the polar ice caps.

Just as ice cores on Earth provide a record of annual changes in climate, the thick stacks of polar ice on Mars have internal layering that suggests they were built up one layer at a time, for millions if not billions of years. (Some of the research I do here at the Museum is directly related to the internal structure of these ice caps, which I mapped out using orbital radar data. I am currently working to understand smaller-scale features buried in the ice.)

So if one of our neighbors may have been habitable in the past, what about our nearest neighbor, Venus?

Venus is almost the same size as Earth, and only slightly closer to the Sun. However, its axis does not tilt relative to the Sun, so it has no seasons like Earth and Mars. We know less about ancient Venus than we do about Mars, because the surface of Venus is relatively young (~1 billion years old). However, we think the atmosphere is much older than the surface, made up of mostly CO2 (like Mars, and like early Earth). With 100 times the atmosphere of Earth, its runaway greenhouse effect long ago boiled all the water off the surface. Some of that water is bound to sulfur and makes up the sulfuric acid clouds that circle the planet, but much of it was broken down in the atmosphere and removed by the solar wind. Venus is dry and hot, despite its clouds reflecting 80% of the sunlight that arrives, since it very effectively traps the remaining 20%.

 

Venus

Clouds swirl around the south pole of Venus, imaged in UV by Venus Express. Image courtesy of the European Space Agency.

So was Venus ever more like Earth?

Being so similar to Earth, Venus likely formed from the same material. The key to their different climates today may be in part due to Earth having plate tectonics, which buries carbon-rich sedimentary rocks (taking CO2 out of the atmosphere). Venus instead keeps all of its CO2 in the atmosphere. The clues to climate change on Venus will probably be found in the composition of its atmosphere, with isotopic ratios of elements like carbon and hydrogen pointing the way to understanding when and why it became so hot and dry.

Only those three inner planets in our Solar System have atmospheres thick enough and persistent enough to have climates that change over time. However, one moon in our Solar System, more massive than the planet Mercury, has an atmosphere. In fact, Titan, a moon of Saturn, was once thought to be the largest moon in the Solar System precisely because its atmosphere is so thick (1.5 times the atmosphere of Earth).

 

Titan

Titan is the only moon in the Solar System with a thick atmosphere, imaged by Cassini. Image courtesy of NASA.

Titan is particularly interesting because its atmosphere is made up mostly of nitrogen, just like the Earth. The remainder is mostly methane, which breaks down easily in the atmosphere and has to be replenished every ~50 million years; this implies some unknown but ongoing process. Titan gets 100 times less sunlight than the Earth, so its surface is frigid, cold enough that water ice is as hard as rock. So while Titan is not currently habitable for life as we know it on Earth, it is the only other place in the Solar System with rain (made of methane and ethane). However, in another 5 billion year the Sun will become a red giant star, and Titan probably will be warm enough to have liquid water on its surface, making it habitable at last.

For the time being, understanding the methane cycle on Titan (perhaps analogous to the water cycle on Earth) will help us understand climate change on Titan, and may give us insight into the behavior of climate on early Earth.

Titan, Venus, and Mars all have something to teach us about the possibilities for climate change and habitability on Earth. While nothing as dramatic as the changes experienced by Mars or Venus is likely to happen anytime soon on Earth, we do know that smaller changes in climate have had big effects on life, and vice versa.

When photosynthesis appeared on Earth ~2.5 billion years ago, it put oxygen into the atmosphere for the first time. When the “snowball Earth” episode ended ~500 million years ago, the warmer and friendlier climate produced macroscopic life for the first time. When extensive volcanism occurred ~250 million years ago, ~95% of life on Earth was wiped out. When the aftermath of a large impact cooled the climate ~65 million years ago, the dinosaurs died off. In the last million years, according to ice core records from Greenland and Antarctica,  recurring periods of warming and cooling (correlated with increasing and decreasing amounts of CO2 in the atmosphere) have caused repeated ice ages and interglacial periods; during the most recent interglacial period (from ~10,000 years ago to today), humanity has thrived.

 

Earth

The one climate in our Solar System that is "just right" for life, imaged by Apollo 17. Image courtesy of NASA.

Currently we are blessed with a friendly climate. What will help us best understand it? What more might we want to know about changes in other climates? What is the role of humanity in the future climate of Earth?

Michelle Selvans is a planetary geophysicist in the Center for Earth and Planetary Studies at the National Air and Space Museum.

Was Mars Ever Habitable?

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If all goes according to plan, on November 25th the Mars Science Laboratory (MSL) rover Curiosity will leave the Earth and begin its journey to Mars. Any delays due to weather or other factors should be accommodated by a launch window that extends until December 18th. The spacecraft will use a new landing system to arrive at its landing site on Mars in August, 2012, and the rover carries an impressive array of scientific instruments. The rover is about twice as large as the Mars Exploration Rovers Spirit and Opportunity, thereby enabling it to navigate terrain characterized by larger obstacles (such as rocks) as it travels up to about 200 meters (219 yards) per Martian day.

 

Curiosity

This artist concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life.

The new landing system for the Mars Science Laboratory replaces the airbag system utilized by the Pathfinder and Mars Exploration Rovers during landing. The new landing system enables much larger rovers and science instrument payloads to be delivered to the surface of Mars than was previously possible and opens the door for future missions geared towards the eventual return of samples for the Red Planet. Upon entering the Martian atmosphere, the MSL spacecraft will first steer itself through the upper atmosphere before deploying a parachute and then using rockets and a tether to lower the Curiosity rover to the surface.

Curiosity’s mission is geared towards understanding whether Mars is or ever could have been habitable. Recent data from NASA’s orbiting spacecraft (Odyssey and the Mars Reconnaissance Orbiter) and the Mars Exploration Rovers suggests the planet has had a long and complicated history of changing environmental conditions and landscapes. Curiosity will follow those missions by deploying a diverse complement of instruments to interrogate the rocks and soils in the vicinity of the landing site. The “next generation” of instruments carried by Curiosity comprises a “mobile laboratory” and should lead to a quantum leap in our understanding of Mars’ potential habitability and how the surface of Mars evolved over time.

landing site

Images of Gale Crater, the selected landing site for the Mars Science Laboratory. The first image shows the regional context of Gale Crater (labeled on the left and discussed above) with colors representing the elevation of the land surface (purple lowest and red highest). The second image shows an example of high priority science targets for exploration near the ellipse (yellow box in first image shows the location) and the last image shows science targets within the target landing ellipse (white box in the first image shows the location).

Advances in landing precision enable consideration of smaller landing sites than was possible during prior missions and made it possible to access the selected landing site within Gale crater. Gale crater is attractive to scientists because there is a five kilometer (three mile)-thick section of layered rocks deemed likely to enable study of changing conditions on Mars over a time when the abundance and duration of water on the surface was decreasing over time. As water is an important factor in evaluating potential habitability, the chance to access the rocks that record the changes from relatively wetter to drier present an opportunity to learn a great deal about Mars as a planet and its potential as a possible abode for life.

Curiosity is an important step in the long term study of Mars and sets the stage for future missions that will be focused on whether there is or ever was life on Mars. By helping to understand whether the planet was habitable and, if so, for how long, MSL will help identify the likely environments and potential targets for future sample return and the eventual search for possible life.

The excitement should begin the day after Thanksgiving, so while resting after eating all that turkey, tune in to NASA TV and watch as Curiosity counts down towards lift-off and the start of an exciting new chapter in our understanding Mars and the solar system.

Visitors to our Museum in DC can also watch the launch, targeted for 10:25 am ET Nov 25, on the giant screen in the Moving Beyond Earth gallery.

John Grant is a geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum, and co-led the process for selecting the landing site for the 2011 Mars Science Laboratory rover.

 

Curiosity Landing Site

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Here is a riddle: What takes more than 60 locations, 5 years, and 150 scientists to decide? The landing site for the Mars Science Laboratory (MSL) rover Curiosity. Picking the landing site for a spacecraft to land on another planet is always serious business. And the job of finding the best location for Curiosity to set down on Mars was no exception.

Curiosity’s mission is geared towards understanding whether Mars could have ever been habitable. And recent data from NASA’s orbiting spacecraft (Odyssey and the Mars Reconnaisance Orbiter) and the Mars Exploration Rovers suggests the planet has had a long and complicated history of changing environmental conditions and landscapes. Combine that with the fact that the landing site could be anywhere between 30 degrees north and south of the equator and below an elevation of 0 kilometers (relative to the Martian datum) and there is a lot of territory to consider.

 

Curiosity Landing Site

This map of Mars shows all of the landing sites proposed for the Mars Science Laboratory (red dots) and the four final candidate sites (blue dots). From the four final sites of Eberswalde crater, Gale crater, Holden crater, and Mawrth Vallis, Gale eventually was selected as the landing site. The white shaded areas are more than 30 degrees north and south of the equator and off limits to MSL because of seasonally harsh (cold) conditions expected there. The black areas are above 0 kilometer in elevation and too high to be considered for landing.

The vast majority of the sites proposed for consideration (Figure 1) were within the general bounds outlined above and many possess attributes making them attractive as possible landing sites. Moreover, the design of the rover enables consideration of a variety of sites. So science merit became the major discriminator of which site would eventually win out.

Over a series of workshops, the science community and MSL science team came together to discuss and evaluate the various proposed sites. The diverse expertise represented at the workshop coupled with ample discussion time ensured each site got a good look. As the process went along, more and more sites were dropped from consideration as potential issues were identified. Finally, four sites remained, all of which were deemed satisfactory for MSL and each with a substantial group of science advocates. These four sites include a relict river delta in Eberswalde crater, a 5 kilometer (3.1 mile) thick section of layered rocks in Gale crater, ancient alluvial and possible lake beds in Holden crater, and ancient sequence of clay-bearing rocks near Mawrth Vallis (Figure 2). The four sites became the focus of intense study and discussion at the final two workshops, with efforts geared towards understanding how the rocks in and near the sites were emplaced and whether they might be accessible to Curiosity once on the ground. As data related to the sites poured in and evaluations went on, the four final sites have become arguably the best imaged and studied locations on the surface of Mars. In the end, there was no “smoking gun” that was found to rule out any of the four final candidate sites and the community reiterated their satisfaction with any one of them. Much more information about each of the proposed landing sites can be found on Marsoweb.

 

Curiosity Landing Site

Summaries of each of the final four candidate landing sites for the Mars Science Laboratory. The left column shows the regional context of each of the four sites (labeled on the left and discussed above) with colors representing the elevation of the land surface (purple lowest and red highest). The middle column shows examples of high priority science targets for exploration near the ellipse (yellow box in left column shows the location of each) and the right column shows science targets within each target landing ellipse (white box in left column shows the location of each). At Eberswalde crater, Curiosity would land on the crater floor and probe ancient river and possible lake beds on the way to a large delta on the western wall of the crater. At Gale crater, the site chosen as the landing site for Curiosity, landing will occur on an alluvial fan near the northern wall of the crater and the rover will than traverse to a thick stack of layered rocks to the south. At Holden crater, landing would take place on broad alluvial fans flanking the western wall of the crater and the rover would traverse down to underlying and finely layered rocks that may have been deposited in a lake. At Mawrth Vallis, landing would occur directly on a layered sequence of clay-bearing rocks that extend regionally across the surface. The images comprising the panels in the middle and right columns are from the HiRISE camera on the Mars Reconnaissance Orbiter. The scale bars in each panel indicate distance in kilometers.

The Curiosity science team then met and considered all of the information related to the sites. Both science potential and risks to rover landing and traversing were considered. In the end, Gale crater was selected as the landing site because the thick section of rocks (Figure 2) was deemed likely to enable study of changing conditions on Mars over a time when the abundance and duration of water on the surface was decreasing over time. As water is an important factor in evaluating potential habitability, the chance to access the rocks that record the changes from relatively wetter to drier present an opportunity to learn a great deal about Mars as a planet and its potential to support life.

Curiosity lifts off towards the Red Planet late in 2011 and will arrive at Mars in mid-2012. In the days and months leading up to landing at Gale crater, the MSL science team will continue to pore over existing and new images to plan the best path towards rocks they feel hold the clues to understanding Mars’ habitability. Once on Mars and on the move, Curiosity will provide images and information from its science payload of instruments that will enable all of us to follow along in the excitement of exploration and learn more about how one of our neighboring planets evolved over time.

John Grant is a geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum and served as the co-chair of the Mars Landing Site steering committee for the Mars Science Laboratory.

A New Curiosity

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There is a strange looking car parked in the west end of the National Air and Space Museum in downtown Washington, DC. For now, it is only visible behind its security screen from the second floor landing above. From that vantage, the vehicle’s six wheels, robotic arm, mast, and other protrusions are clearly visible. But since this is the Air and Space Museum, it must be more than just a normal car.

Soon the barriers will be gone and the public will be able to view the vehicle up close and personal. And what they will see is a model of the next Mars rover, NASA’s 2011 Mars Science Laboratory. The rover, dubbed “Curiosity” will be launched to Mars later this year and will begin its mission to explore whether places on the Red Planet were ever habitable. Information on the mission can be found at: http://marsprogram.jpl.nasa.gov/msl/. The rover carries a suite of instruments geared towards understanding conditions on the planet and a full description of the payload can be found at: http://marsprogram.jpl.nasa.gov/msl/mission/instruments/.

NASA Mars Rover Curiosity at JPL, Side View. The rover for NASA's Mars Science Laboratory mission, named Curiosity, is about 3 meters (10 feet) long, not counting the additional length that the rover's arm can be extended forward. The front of the rover is on the left in this side view. The arm is partially raised but not extended. Rising from the rover deck just behind the front wheels is the remote sensing mast. Image Credit: NASA/JPL-Caltech

The landing site for Curiosity will be one of four final candidate sites all deemed to possess a variety of features suited to evaluating whether Mars could have been habitable in the past. It is expected that NASA will announce the landing site in the coming weeks. Much more information on the landing sites proposed for Curiosity can be found at: http://marsoweb.nas.nasa.gov/landingsites/index.html.

The model of Curiosity will be on display through Labor Day of this year.

See the model of Curiosity and learn more about its mission at this year’s Mars Day! on July 22.

John Grant is a geologist in the Museum’s Center for Earth and Planetary Studies and co-chair of the Mars Landing site steering committee leading the MSL landing site selection process.

A ‘Spectacular’ Hoax Continues to Fool E-mail Readers

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As an astronomy educator here at the National Air and Space Museum, I’ve had the opportunity to interact with thousands of visitors, especially in our Public Observatory. I’ve enjoyed the many chances to discuss the wonders of the Universe and to answer visitors’ astronomy-related questions. However, I tend to dread the month of August because of an internet hoax involving Mars that’s been plaguing e-mail inboxes for seven years.

The e-mail in question is commonly referred to as the “Mars Hoax” or, more accurately, the “Mars Spectacular,” and is titled: “Two moons on 27 August or The Red Planet is about to be spectacular!”

It informs recipients that Mars will have an extremely close encounter with Earth during the month of August, culminating on August 27th when Mars is approximately 34 million miles away. The information in the previous sentence was only true during the month of August in 2003. This was a historic astronomical event. Mars was the closest it had been to Earth in 60,000 years. However, this already happened.

Before I get into the e-mail’s misinformation, let’s talk about what actually happens when Earth and Mars have a close encounter. Imagine two people are running a race around a track. One person is running in the innermost lane while the other is running in the outermost lane. The runner in the inside lane will complete one lap faster than the other person. This is similar to Earth’s and Mars’ orbits around the Sun. Earth takes 365 days to complete a lap around the Sun while Mars completes a lap in 687 days. If the runners continue running, eventually the runner on the inside (Earth) will catch up with the runner on the outside (Mars). When this occurs in the solar system, it is called opposition. It also means that Mars is opposite of the Sun in the Earth’s sky. An opposition for Mars occurs approximately every 2 years. The last three occurred on November 7, 2005, December 24, 2007, and most recently on January 29, 2010.

Opposition of Mars

An opposition occurs when the Sun, Earth and Mars line up with the Earth in the middle. This phenomenon, which happens every two years, brings Earth and Mars relatively close together. This diagram shows four recent oppositions and two future ones. The 2003 opposition was significant because Mars was very near its perihelion - the point in its orbit where it is closest to the Sun. At that time, Mars came within 35 million miles of Earth. Mars will be almost that close again during the opposition in July of 2018.

Why was the Mars opposition in 2003 so special? Most oppositions bring Earth and Mars between 34 and 63 million miles from each other. This is mainly due to Mars’ elliptical orbit. All planetary orbits are slightly elliptical meaning that a planet’s distance to the Sun changes as it moves in its orbit. When it’s closest, it’s called “perihelion” and when farthest, “aphelion.” Mars’ orbit is more elliptical than Earth’s. Every 15 to 17 years, Mars is in, or very close to, its perihelion point just as Earth “catches up” with Mars. This brings the two planets especially close together. In 2003, this perihelic opposition occurred on August 27, when Mars was closest to the Sun, and Earth near its most distant point from the Sun. This combination brought the Earth and Mars unusually close together. As a result, Earth and Mars were 34.6 million miles away from each other; the closest they had been in 60,000 years.

If you missed this historic event, you may be wondering what Mars looked like in the sky during August of 2003. According to the most recent versions of the Mars Spectacular e-mail, Mars will appear “as large as the full moon to the naked eye.” That’s huge! No wonder people are still excitedly forwarding this e-mail to everyone they know. The original e-mail, though, stated, “At a modest 75-power magnification Mars will look as large as the full Moon to the naked eye.” This is more or less true, just misleading. It’s referring to how Mars could appear if magnified 75 times by a telescope eyepiece. To see any significant detail on the Martian surface rather than a large, red, fuzzy blob one would have to peer through a telescope with an objective mirror or lens larger than 8 inches; a much larger telescope than what department stores sell.

Mars in the Night Sky

On August 27, 2003, Mars appeared as a bright star in the night sky. Even during this record approach it did not appear as large or as bright as the full Moon. Photo credit: John Nemy & Carol Legate of Whistler, B.C.

To the naked eye, Mars appeared as a bright, reddish, star-like object during the 2003 opposition. It was twice as bright as Sirius, the brightest star in the night sky, but not quite as bright as Venus appears this month. Compared to the full Moon, Mars was only 1/75 of its size – certainly not a second Moon in the sky. Those who forward the Mars Spectacular e-mail probably don’t consider the implications of Mars appearing that large. Mars is around twice the size of our Moon. It would be have to be located at twice that distance (480,000 miles) for it to appear the same size – 33 million miles closer than it ever gets to Earth. If Mars does appear as our “second moon,” something has gone terribly wrong with the inner solar system or the laws of physics .

Mars Hoax

Some versions of the e-mail, referred to as the "Mars Spectacular" are in the form of a PowerPoint presentation. This particular (and completely untrue) slide has evolved from a misleading statement claiming that Mars will appear as large as the full Moon through a modest telescope.

The Mars Spectacular e-mail is still circulating. I know three people who received it in the past month from well-meaning relatives. One reason it still has life is because the actual year of the event was dropped from the e-mail text. Therefore, every August people receive this e-mail and believe Mars will be close to Earth that year. Unfortunately, “2010” has mysteriously appeared in recent versions of the e-mail which definitely does not allow the e-mail to go away quietly.

If you have received the Mars Spectacular e-mail, believed it to be true, and passed it along to friends, family, or perhaps even a news outlet, it’s okay. You’re not the first one to fall for its thrilling message and you certainly won’t be the last. A good lesson to come from the Mars Spectacular e-mail is: if it’s too fantastic to be true, it’s probably not. Being internet savvy means you know where to find trustworthy sources and can weed out the misinformation. To check the validity of e-mail content, one of the best online resources is Snopes. You’ll find the “Mars Hoax” in the #12 spot of their Hot 25 list of urban legends. NASA, as well as astronomy magazine sites such as Sky and Telescope and Astronomy are also good online astronomy resources.

Disappointed that you won’t be able to see a “spectacular” Mars? Don’t fret! Mars is viewable in the evenings throughout the month of August, 2010. It is currently low in the southwestern horizon after sunset, hanging out with Saturn and a very bright Venus. Check Sky & Telescope’s weekly “sky at a glance” page for observing tips and information on other astronomical events.

Shelley Witte is an astronomy educator at the National Air and Space Museum.