Mars and Venus

Mars and Venus are the two terrestrial planets most similar to Earth. One orbits closer to the Sun, and one orbits more distant to the Sun. But both are visible with the unaided eye, and two of the brightest objects in the night sky.

Venus orbits at an average distance of only 108 million km from the Sun, while Mars is an average of 228 million km. Venus gets as close to Earth as 38 million km, and Mars gets as close as 55.7 million km.

In terms of size, Venus is almost a twin planet of Earth. Its diameter is 12,104 km, which is 95% the diameter of Earth. Mars is much smaller, with a diameter of only 6,792 km. And again, in terms of mass, Venus is almost Earth’s twin. It has 81% the mass of Earth, while Mars only has 10% the mass of Earth.

The climates of Mars and Venus are very different, and very different from Earth as well. Temperatures on the surface of Venus average 461 °C across the entire planet. That’s hot enough to melt lead. While the average temperature on Mars is a chilly -46 °C. This temperature difference comes from the fact that Venus is closer to the Sun, but also because it has a thick atmosphere of heat trapping carbon dioxide. The atmosphere on Venus is nearly 100 times thicker than Earth’s atmosphere at sea level, while the atmosphere on Mars is 1% the thickness of Earth.

Mars is the most studied planet in the Solar System (after the Earth). There have been dozens of missions sent to Mars, including orbiters and rovers. Although many missions have been lost, there have been several that have successfully orbited the planet and several that have landed on the surface. Missions have also been sent to Venus, and you might be surprised to know that the Soviets sent a series of landers called Venera that actually reached the surface of Venus and survived long enough to send back a few photographs.

Mars has two moons, Phobos and Deimos, while Venus has no moons. And neither planet has rings.

We’ve written many articles about Mars and Venus for Universe Today. Here’s an article about how the atmospheres of Mars and Venus leak into space, and a look at Venus wet past.

If you’d like more information on those two planets, here’s a link to NASA’s Solar System Exploration Guide on Venus, and Hubblesite’s News Releases about Mars.

We’ve also recorded several episodes of Astronomy Cast about the planets. Listen here, Episode 50: Venus and Episode 52: Mars.


Mars Pathfinder

Mars Pathfinder was NASA mission to Mars, which launched on December 4th, 1996 and landed on the surface of Mars on July 4, 1997. Unlike the missions that went before it, the Pathfinder lander was also equipped with a tiny rover called Sojourner, which could venture away from the lander, crawl around the surface of Mars and study rocks up close. It was a relatively inexpensive mission that tested out many of the technologies build into later missions, like the Mars Exploration rovers Spirit and Opportunity.

The purpose of Pathfinder was to prove that the concept of “faster, better and cheaper” missions would work. Pathfinder only cost $150 million and was developed in under 3 years. It was also sent to study the surface of Mars, including the geochemistry of the rocks, the magnetic properties of the surface and the structure of the planet’s atmosphere.

When the Pathfinder mission arrived at Mars, it entered the atmosphere and deployed a parachute. Instead of using retrorockets to land gently on the surface, however, Pathfinder used an airbag system. This allowed it to save fuel; instead of landing gently, it was dropped from an altitude of about 100 meters onto the Martian surface. It bounced several times and came to a rest before opening up like the petals of a flower. Once everything checked out, the tiny Sojourner Rover was deployed onto the surface of Mars.

The area around the Pathfinder site had many rocks, large and small, and the NASA scientists gave them unique names like “Barnacle Bill” and “Yogi”. Sojourner was able to crawl around and study these rocks up close. It was able to study the chemical makeup of the rocks, and confirmed that they formed from past volcanic activity. Over the course of the entire mission, Pathfinder and Sojourner returned 16,500 images and made millions of measurements of the Martian atmosphere.

Pathfinder stopped communicating with Earth after 83 days on the surface of Mars. Its battery was only designed to be recharged 40 times, and once its battery stopped working, the spacecraft was unable to keep its electronics heated in the cold Martian night. After it stopped communicating, NASA decided to name the lander after Carl Sagan. It became The Carl Sagan Memorial Station.

We have written many articles abut the Mars Pathfinder mission for Universe Today. Here’s an article about photos of Mars Pathfinder taken from orbit, and research about a cold and wet early Mars.

Here’s a link to the original mission homepage for the Mars Pathfinder.

We’ve recorded several episodes of Astronomy Cast about missions to Mars. Start here, Episode 92: Missions to Mars, Part 1.

Source: NASA

Who Discovered Mars?

Mars is one of the 5 planets visible with the unaided eye. On any dark night, when Mars is in the sky, it’s easy to see with your own eyes. Ancient people knew about Mars, and long ago discovered that it moves from night to night compared to the stars. So it’s impossible to know who discovered Mars. That would have been one of the first humans.

Perhaps a better question to ask is: who realized that Mars is a planet? And that discovery happened with the idea that the Earth is a planet.

In ancient times, astronomers thought that the Earth was the center of the Universe, and the Sun, Moon, planets and stars orbited around us in a set of crystalline spheres. But the motions of the planets were hard to explain; they would sometimes speed up, stop, and even reverse their direction in the sky.

But the astronomer Nicolaus Copernicus developed the view that it was the Sun that was at the center of the Solar System, and the planets orbited around it. This view neatly explained the strange motions of the planets, since the Earth was also moving around the Sun, and these quirks were really just changes in perception.

Galileo was the first person to view Mars in a telescope, and he saw not much more than a bright disk. He did take many observations over the course of the year and realized that Mars gets closer and more distant, and so larger and smaller in his telescope. As telescopes got bigger and better, astronomers were able to make out the polar ice caps on Mars, and some astronomers incorrectly thought they saw a system of canals crisscrossing the surface of the planet.

But the best views of Mars came with the first robotic exploration of Mars. The first spacecraft to arrive at Mars was NASA’s Mariner 4, launched in 1964. The first spacecraft to go into orbit around Mars was Mariner 9, in 1971. These spacecraft helped take high resolution images that revealed craters, mountains and chasms; the red landscape of Mars that we’re so familiar with today.

We’ve written many articles about the discovery of planets for Universe Today. Here’s an article about the discovery of Uranus, and another about the discovery of Neptune.

If you’d like more information on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We’ve also recorded several episodes of Astronomy Cast about Mars. Start here, Episode 52: Mars.

NASA Mars Exploration
NASA: The Mariner Missions

New Findings On Allen Hills Meteorite Point to Microbial Life

Scientists caused quite a stir in 1996 when they announced a meteorite had been found in Antarctica that might contain evidence for microscopic fossils of Martian bacteria. While subsequent studies of the now famous Allen Hills Meteorite shot down theories that the Mars rock held fossilized alien life, both sides debated the issue and the meteorite is still being studied. Now, Craig Covault in reports that a new look at ALH84001 provides “evidence that supports the existence of life on the surface of Mars, or in subsurface water pools, early in the planet’s history.” Covault says we can expect a public announcement by NASA Headquarters within a few days.

Research using a more advanced High Resolution Electron Microscopy than was in existence when the initial findings were made 13 years ago has provided the new evidence. Covault reported that the “laboratory sensors are being focused directly on carbonate discs and associated tiny magnetite crystals present inside the meteorite Allen Hills ALH 84001.” The data reveal information that counters a “wide range of opposing theories as to why the finding should not be supported as biological in origin.”

The new findings were reported in the November issue of the respected journal Geochimica et Cosmochimica Acta, the journal of the Geochemical and Meteoritic Society. The authors include Kathie Thomas-Keprta, Simon Clement, David McKay (who led the original team), Everett Gibson and Susan Wentworth, all of the Johnson Space Center.

Covault said the new work centers on what is called magnetic bacteria that on Earth, and Mars as well, leave distinctively-shaped remnants in the rock. These features test with a high chemical purity more like a biological feature than geological.

For more details, read the article on

Exciting! Stay tuned…

Cold as Hell with a Chance of Dust Storms: Weather Movies from Mars

If you think about it, those hypnotizing patterns of swirling clouds you see in TV weather reports are pretty amazing: satellites let us see what’s happening in the skies all over the world. But these days, that kind of global vision even goes beyond the Earth. The Mars Reconnaissance Orbiter makes daily weather observations of the Red Planet, and mission scientists regularly compile the pictures into movies that are available online. The result is that anyone can follow along as fierce dust storms rage across the plains of Mars, clouds cling to the peaks of towering volcanoes and polar ice advances and retreats.

On board the MRO is a wide-angle camera called the Mars Color Imager (MARCI) that scans the face of Mars in both visible and ultraviolet light. MARCI views Mars from pole to pole, snapping dozens of images every day that are combined into a global map with resolution comparable to weather satellites at home.

This daily weather report helps Mars explorers understand day-to-day events, as well as seasonal and annual changes on the Red Planet. Sometimes the weather watch also gives rover drivers a crucial warning when a storm might be headed in the direction of Spirit or Opportunity.

The weather images can be striking and intriguing. This animation shows the south pole of Mars during a period of about a month earlier this year, when storms raged along the retreating edge of frost in the polar cap. You can see giant, swirling clouds of dust, as well as the changing shape of the cap as it shrinks with the approach of Summer.

Malin Space Science Systems is the firm that built and operates MARCI for NASA’s Jet Propulsion Laboratory. They post weekly movies that show a spinning, global view of the most recent Martian weather. You never know what you’ll see each week, but a careful look often turns up water ice clouds, wind storms or the giant canyon Valles Marineris filled to the brim with dust.

The descriptions that Malin scientists write to accompany each movie are fascinating. They sound both as exotic as a science fiction novel–and as routine as your local weatherman’s report on the evening news. One sample:

“A large dust storm moved south down the Acidalia/Chryse/Xanthe corridor, partially spilling into eastern Valles Marineris at the beginning of the week. From there the storm moved over Thaumasia and Argyre, picking up intensity as it moved into the subtropics of Aonia and Icaria/Daedalia… Dust storms and water-ice clouds also formed in the northern mid-latitudes, with more notable activity occurring over Deuteronilus and Utopia. The increased amount of dust activity on the planet has created a haze that lingers in the atmosphere and has caused skies over both Opportunity and Spirit to be hazy during the past week.”

That’s why Mars fascinates. It’s an alien world that in some ways is tantalizing similar to home.

MARCI will be turned back on in early December after a hiatus of a few months. Previous weather movies are still online.

Large Ocean, Extensive River Network, Rainfall on Ancient Mars

Did Mars once have a vast network of river valleys – “canals” if you will – and an ocean that covered most of the planet’s northern hemisphere? A new computer-generated map of the Red Planet provides a more detailed look at the valley networks on Mars, and indicates the networks are more than twice as extensive as had been previously depicted in the only other planet-wide map of the valleys. “All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars,” said Wei Luo, from Northern Illinois University (NIU). “It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet’s surface.”

This is a global map depicting the dissection density of valley networks on Mars, in relation to the hypothesized northern ocean.  Credit: NIU, LPI
This is a global map depicting the dissection density of valley networks on Mars, in relation to the hypothesized northern ocean. Credit: NIU, LPI

NIU and the Lunar and Planetary Institute in Houston used an innovative computer program to produce the new map that shows regions dissected by the valley networks roughly form a belt around the planet between the equator and mid-southern latitudes, consistent with a past climate scenario that included precipitation and the presence of an ocean covering a large portion of Mars’ northern hemisphere.

Scientists have previously hypothesized that a single ocean existed on ancient Mars, but the issue has been hotly debated.

Luo and Tomasz Stepinski, a staff scientist at the Lunar and Planetary Institute, publish their findings in the current issue of the Journal of Geophysical Research — Planets.

“The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean,” Stepinski said.

The researchers created an updated planet-wide map of the valley networks by using a computer algorithm that uses topographic data from NASA satellites and recognizes valleys by their U-shaped topographic signature. “The basic idea behind our method is to flag landforms having a U-shaped structure that is characteristic of the valleys,” Stepinski added. “The valleys are mapped only where they are seen by the algorithm.”

Valley networks on Mars exhibit some resemblance to river systems on Earth, suggesting the Red Planet was once warmer and wetter than present.

The networks were discovered in 1971 by the Mariner 9 spacecraft, but scientists have debated whether they were created by erosion from surface water, which would point to a climate with rainfall, or through a process of erosion known as groundwater sapping. Groundwater sapping can occur in cold, dry conditions.

The large disparity between river-network densities on Mars and Earth had provided a major argument against the idea that runoff erosion formed the valley networks. But the new mapping study reduces the disparity, indicating some regions of Mars had valley network densities more comparable to those found on Earth.

A zoomed-in area comparing the old map of valley networks and the new one. (Left) A satellite image, with color indicating elevation; (center) the old map of valley networks; (right) the new map of valley networks.  Credit: Wei Luo, Northern Illinois University
A zoomed-in area comparing the old map of valley networks and the new one. (Left) A satellite image, with color indicating elevation; (center) the old map of valley networks; (right) the new map of valley networks. Credit: Wei Luo, Northern Illinois University

“It is now difficult to argue against runoff erosion as the major mechanism of Martian valley network formation,” Luo said. “When you look at the entire planet, the density of valley dissection on Mars is significantly lower than on Earth,” he said. “However, the most densely dissected regions of Mars have densities comparable to terrestrial values. The relatively high values over extended regions indicate the valleys originated by means of precipitation-fed runoff erosion—the same process that is responsible for formation of the bulk of valleys on our planet.”

“The only other global map of the valley networks was produced in the 1990s by looking at images and drawing on top of them, so it was fairly incomplete and it was not correctly registered with current datum,” Stepinski said. “Our map was created semi-automatically, with the computer algorithm working from topographical data to extract the valley networks. It is more complete, and shows many more valley networks.”

The Martian surface is characterized by lowlands located mostly in the northern hemisphere and highlands located mostly in the southern hemisphere. Given this topography, water would accumulate in the northern hemisphere, where surface elevations are lower than the rest of the planet, thus forming an ocean, the researchers said.

“Such a single-ocean planet would have an arid continental-type climate over most of its land surfaces,” Luo said.

The northern-ocean scenario meshes with a number of other characteristics of the valley networks.

“A single ocean in the northern hemisphere would explain why there is a southern limit to the presence of valley networks,” Luo added. “The southernmost regions of Mars, located farthest from the water reservoir, would get little rainfall and would develop no valleys. This would also explain why the valleys become shallower as you go from north to south, which is the case.

“Rain would be mostly restricted to the area over the ocean and to the land surfaces in the immediate vicinity, which correlates with the belt-like pattern of valley dissection seen in our new map,” Luo said.

Source: EurekAlert

Want to be a Martian?

If you’ve ever dreamed of exploring Mars, but are worried about all that pesky radiation exposure and being cramped in a capsule for the two-year flight – or about never coming back – then your dream may be realized with NASA’s “Be a Martian” web site. In the spirit of other citizen scientist collaborations such as Galazy Zoo and [email protected], NASA has created a site that allows you to view and categorize images to help map the Martian surface from the safety of your own home here on Earth.

The Be a Martian site is a collaboration between NASA and Microsoft that uses the tool of crowsourcing to sift through the hundreds of thousands of photos sent back by Mars rovers and orbiters. The format of the site is much like a game, where you complete tasks to earn points and badges.

There are two types of classifying activities to do on the site: count craters and match up images. Counting craters is just like it sounds: you are presented with an image, and place markers on any craters that you see. Counting craters in small regions on the Martian surface will help scientist determine the relative age of these regions – the more craters, the older an area is likely to be.

The image mapping is a bit trickier, though, because you have to match up 2-3 small, but high resolution images onto the background of a larger, much lower resolution image. The user starts in Vallis Marinaris, but can move onto other parts of Mars from there. By helping map the surface, better maps of the surface can be made to help scientists interpret the changing conditions of Mars.

Being a Martian citizen also has some civic responsibilities, too. There is a forum on the site where one can ask questions, vote on questions and make comments to earn “Curiousity Points”. NASA Mars experts will read the questions to see what the virtual Martian community is interested, and will host town hall-type meetings in the future where members can participate.

“We really need the next generation of explorers. And we’re also accomplishing something important for NASA. There’s so much data coming back from Mars. Having a wider crowd look at the data, classify it and help understand its meaning is very important,” Michelle Viotti, from the Jet Propulsion Laboratory told BBC News.

Extras are also available on the site, including wallpapers, mission overviews, and videos. You’ll need to have Microsoft’s Silverlight application for the games and videos on the site to work.

So, if you aren’t already completely addicted to Galaxy Zoo or any other citizen scientist site, now’s your chance! Oh, and if you want your Martian name to be Marvin, too bad – I tried, and it’s already been taken!

Source: Be a Martian, NASA

Spirit Extrication, Day 1: Drive Stopped After 1 Second

Mission managers sent the drive commands to the Spirit rover at 4 a.m. EST (0900 GMT) today, — Nov. 17, 2009 and Sol 2088 for the rover — but the data back from the rover indicates the rover stopped less than one second after it began moving its wheels when the rover automatically sensed more lateral tilt than permitted. A tight limit on vehicle roll and pitch of less than 1 degree change was set for this first drive, and as the rover began its first move, it sensed that its roll was outside the allowed limit and safely stopped the drive. Those driving the rover say they are starting cautiously, setting initial parameters with very tight limits with the knowledge that these hair triggers may stop the rover frequently. As the project gains confidence with extrication, these limits may be relaxed. From this limited drive the team now has a more accurate measurement of vehicle roll and pitch that will be used for subsequent drive planning. Analysis is continuing. The team hopes to completion their planning of the next drive on Wednesday, Nov. 18, with possible wheel movement again on the 19th (Sol 2090)

At last week’s press conference about the attempt to extricate Spirit from the Martian sand trap, the rover team stressed this procedure could take weeks or months, with the likelihood of not being successful.

Learn more about the process in this video footage of the rover testing and planning teams.

Source: Free Spirit

Ok, Spirit Rover, Let’s Blow This Pop Stand!

On Monday, Nov. 16, NASA will begin transmitting commands to the Spirit rover on Mars to begin the extrication process to free the rover from where she has been stuck since April 23rd of this year. While members of the rover team have not given up on getting the rover to rove again, they were very guarded at a press conference Thursday in showing any optimism about removing Spirit from her predicament. “Spirit is facing the most challenging situation we have seen on Mars,” said Doug McCuistion director, Mars Exploration Program. “We know a lot of people view Spirit with great affection, and have followed along with the mission and seen new vistas and landscapes along with the rover to uncover new knowledge about our sister planet. But I want everybody to be realistic. This is a serious situation and if it cannot make the great escape from this sandtrap its likely this lonely spot might be where Spirit ends its adventures on Mars.”

John L. Callas, project manager for the rovers said the commands will be sent to Spirit on Monday night, the first drive will be executed early Tuesday, and they should find out later on Tuesday if any progress was made. But don’t expect anything to happen fast. “This is going to be like watching grass grow,” Callas said. “We’ll drive and then follow each drive with detailed analysis to see if it is on trend to what we are expecting. The reality is, we will see very little motion at least initially.”

Callas added that although the rover team has worked for months in the a test bed on Earth with an engineering model of the rover to develop a technique for extricating Sprit, there is no Earth analog for what is going on at Mars. “Spirit is on a planet with almost no atmosphere, 3/8 gravity of Earth, and a vehicle with hard metal wheels that only goes about 2 inches a second. We can’t rock back and forth and take advantage of momentum, and spin the wheels as we steer, like someone would do to get a stuck car out on Earth.”

Spirit's location. Image Credit: NASA/JPL-Caltech/Cornell/Ohio State University/University of Arizona
Spirit's location. Image Credit: NASA/JPL-Caltech/Cornell/Ohio State University/University of Arizona

The plan is to attempt to drive the rover forward, which is actually backward, since the rover was driving in reverse when it entered this area where it broke through a “duricrust” and fell through to the talcum powder-like soil. Rover driver Ashley Stroupe said going forward is better because the rover won’t have to break new ground; it will just follow the tracks back out. Plus, then the rover doesn’t have to climb vertically, and if it makes enough progress, eventually it will be heading downhill.

The team did have some good news to share: the “amnesia” Spirit has been experiencing with its flash memory may have been fixed, at least for now. The drive was reformatted and at appears to be working well.

The team said they would try working to remove the rover at least until February before throwing in the towel. A mission review is scheduled at that time.

However, if the rover is destined to remain in this spot forever, lead scientist Ray Arvidson says that’s not all bad. “No place is a nice place to be embedded, but this place is a geological treasure trove,” he said. “The soil is coarse sand with highest sulfate content we have found yet on Mars. Spirit is sitting astride a geological boundary, (see top image — they believe Spirit is sitting on the edge of a small impact crater) and it’s an exciting area to be in scientifically.”

Bright soil stirred up by the rover wheels. Credit: NASA/JPL/University of Arizona
Bright soil stirred up by the rover wheels. Credit: NASA/JPL/University of Arizona

Callas said the solar panels are currently at about 60% performance and if no big dust accumulation occurs, Spirit should be able to make it through the next winter if she remains where she is. “But if environmental things change, that could be a problem,” Callas said. “We’re ok now but we really have no margin on that.”

Stay tuned!

Stuck Spirit Rover Moves!

The Spirit Rover, which has had its wheels stuck for 145 Martian sols, has finally moved! Though she’s far from being extricated from her current position, this is the first time that she’s budged in quite a while. The Mars rover driving team is working on ways to get Sprit out, and this recent move was just them getting Spirit’s wheels in alignment for an upcoming procedure to free her from the sand trap she’s stuck in. But it’s a start!

As Emily reported over at the Planetary Society Blog, this is the “First drive sequence in 145 sols”, according to the rover driver Scott Maxwell on Twitter. The team is getting ready to start extricating Spirit.

The rover team has been working diligently on ways to get Spirit free from the sand that the rover has been stuck in since April. Given that the rover has been having memory problems – the most recent was October 30th – this will be an extraordinary challenge.

Here are some more animations of Spirit’s most recent move:

This is from Spirit's forward hazcam, from sols 2078 and 2079. You can see the buried wheel in the bottom left portion of the image. Credit: NASA / JPL / animation by Damien Bouic
This is from Spirit's forward hazcam, from sols 2078 and 2079. You can see the buried wheel in the bottom left portion of the image. Credit: NASA / JPL / animation by Damien Bouic
Spirit's right rear hazcam from sols 2072 to 2078. Image Credit: NASA / JPL / animation by fredk
Spirit's right rear hazcam from sols 2072 to 2078. Image Credit: NASA / JPL / animation by fredk

NASA will be giving out further details of their plan at a press conference this Thursday, November 12th , so be sure and check back here for more specific information on the escape plan for Spirit!

Source: Planetary Society Blog