Posted on by Nicholos Wethington

Matching Cyclone Found at Saturn’s North Pole

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Cassini keeps on brining us surprises from Saturn and its moons. Recently, it helped us narrow down the length of a day on Saturn. Now, infrared data from the spacecraft confirms a hot, hexagonal cyclone spinning away at the north pole of of the planet.

The south polar hot spot had been previously observed, and was thought to be due to the sunny conditions, as this region of Saturn is currently in summer. Observations from the Cassini spacecraft in early 2007 revealed that Saturn also has a hot cyclone spinning away at the north pole, despite the fact that this region hasn’t seen the Sun in over 10 years.

Voyager 1 and 2 took observations of the north pole in the 1980s, but the Cassini data gives a more detailed view of the features. It was thought that the sunlight was causing the hot spot at the south pole.This new data, though, adds a bit of mystery to the mechanisms causing the cyclones. They appear to be permanent fixtures of the planet, rather than caused by the seasons.

“The hot spots are the result of air moving polewards, being compressed and heated up as it descends over the poles into the depths of Saturn. The driving forces behind the motion, and indeed the global motion of Saturn’s atmosphere, still need to be understood,” said planetary scientist Leigh Fletcher of the University of Oxford, England, and lead author of the paper published in Science on January 4th.

The northern cyclone also has the peculiar shape of a hexagon, something absent from the southern cyclone. The recent findings place the hexagon higher up in the clouds than previously shown, though the cause of the curious shape is still unexplained.

Neptune is home to a hot spot on its southern pole, and the Great Red Spots on Jupiter is another example of long-lasting cyclonic features on a gas giant. Knowing more about the cyclones on Saturn will help us understand similar weather patterns on the other gas giants.

Winter lasts 15 years on Saturn, and in the next few years the north pole will again start to see sunlight, possibly changing the features of the cyclone and giving scientists a better understanding of how the Sun affects these tricky twisters.

Source: JPL Press Release

Posted on by Nicholos Wethington

Organic Molecules Found Outside our Solar System

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Organic molecules are thought by scientists to be instrumental in kickstarting life as we know it on Earth. Within our Solar System they can be found in comets, and they cause the redness of the clouds of Saturn’s moon Titan. New observations of a planet-forming disk around a star 220 light-years from Earth reveal for the first time that these molecules exist elsewhere in the Universe.

Astronomers at the Carnegie Institute have detected the presence of organic molecules in the dusty disk surrounding HR 4796A, an eight-million year-old star in the constellation Centaurus. Using Hubble’s Near-Infrared Multi-Object Spectrometer they analyzed the light coming from the disk and found that its red color is due to large organic carbon molecules called tholins. The analysis ruled out other causes of the red light, such as iron oxide.

“Until recently it’s been hard to know what makes up the dust in a disk from scattered light, so to find tholins this way represents a great leap in our understanding,â€? said John Debes of the Carnegie Institute’s Department of Terrestrial Magnetism, one of the authors of the study.

Just as in our early Solar System, the disk of dust is in the process of forming planets. The collision of small bodies like asteroids and comets creates the dust in the disk, and the organic molecules present on these objects could then be scattered on any planets orbiting the star. This discovery makes it clear that it is possible for organic molecules to exist in the early stages of planet formation, paving the way for the possible development of life later on.

Organic molecules are thought to be essential to the development biological organisms because they are made up of carbon, the building block of life on Earth. The discovery of these molecules elsewhere in the Universe does not mean that life exists there yet – or even that it will in the future – but it does increase the tantalizing prospect of life forming outside our Solar System.

The study was published in the current Astrophysical Journal Letters by John Debes and Alycia Weinberger of the Carnegie Institution’s Department of Terrestrial Magnetism with Glenn Schneider of the University of Arizona.

Source: Carnegie Institute Press Release

Posted on by Nicholos Wethington

Magnetic “Ropes” Connect the Northern Lights to the Solar Wind

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This discovery comes just in time to light up Christmas: new observations of the Northern Lights – a spectacular phenomenon that lights up the night sky – show them to be more intricate than previously thought.

The Northern Lights were observed by NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS), a system of ground cameras and five orbiting micro-satellites that work in combination to observe the phenomenon better than with a single satellite. This allowed scientists to map and understand the mechanisms of the Northern Lights better than before by giving them a 3D picture of the events.

The Northern Lights or “Aurora Borealis” occur when charged particles coming from the Sun interact with the Earth’s magnetic field. THEMIS found evidence that there are magnetic “ropes” — long, wound magnetic field lines that resemble the braids of a rope – connecting the Earth’s magnetic field with the solar wind. Particles are channeled through these ropes, which last a short time, and are focused in certain regions, boosting the energy of the Aurora Borealis.

“THEMIS encountered its first magnetic rope on May 20,” said David Sibeck, project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, MD. “It was very large, about as wide as Earth, and located approximately 40,000 miles (70,000 km) above Earth’s surface in a region called the magnetopause.”

The magnetopause is where the Earth’s magnetic field meets the solar wind.

Electromagnetic explosions were also observed by THEMIS at the bow shock of the Earth’s magnetic field. The bow shock is where the magnetosphere bunches up as the Earth travels through space, kind of like how the waves in the front of a boat moving through the water are closer together than those behind the boat.

Sibeck said of the explosions,”It is where the solar wind first feels the effects of Earth’s magnetic field. Sometimes a burst of electrical current within the solar wind will hit the bow shock and – Bang! We get an explosion.”

The results were presented at the meeting of the American Geophysical Union in San Francisco this month. THEMIS will continue to observe the Aurora Borealis over the next two years, taking measurements of ions, electrons and electromagnetic radiation in space. Scientists from the US, Canada, Western Europe, Russia and Japan are contributing to the study of Earth’s own Christmas lights.

Original Source: NASA Press Release

Posted on by Nicholos Wethington

How Long is a Day on Saturn?

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If you were on the surface of Saturn, how long would a day last? This has remained a mystery for scientists, because the thick clouds of gas obscure the surface of the planet from direct observation by telescopes or orbiters. Below all those clouds there is a surface that rotates at a constant speed. Since scientists can’t directly see the surface, they’ve taken another approach: listening.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

With the help of radio emissions that come from the interior of Saturn, scientists have been able to close in on its rotation period. Charged particles trapped in the interior emit radio waves when they interact with Saturn’s magnetic field, at about 100 Kilohertz. It’s as if Saturn had its own radio station broadcasting at a certain frequency, and as the magnetic field deep inside the planet rotates it changes the frequency of the station.

Voyager measured these emissions for nine months when it passed by in the 1980s, and the rotation was calculated to be 10 hours 39 minutes 24 seconds, with an uncertainty of 7 seconds. The Ulysses spacecraft also monitored the emissions 15 years later, and came up with a result of 10 hours 45 minutes 45 seconds, with a 36 second margin of error.

Wait, that’s 6 minutes of difference! Either Saturn slowed down a lot over the years, or something else is going on. Cassini has been measuring these same radio emissions with its Radio and Plasma Wave Science instrument, and has observed that in addition to this long-period variation, the rotation differs by as much as one percent in a week.

Scientists think that this could be due to two different things: the solar wind coming from the Sun is interfering with the measurements, or particles from Enceladus’ geysers are affecting the magnetic field. Both of these would cause the radio emissions to vary, and they could be causing the different results simultaneously.

Cassini’s new data strongly suggests that the solar wind is a likely culprit: there is a variation in the measurements of the short-period rotation every 25 days, which corresponds with the rotation of the Sun as seen from Saturn. The speed of the solar wind, too, varies the measurements, so must be accounted for. Enceladus could be the cause of the long-term difference, but more measurements are needed to see if this is definitely the case, or if there is yet another factor.

Nailing down the rotation of Saturn will be helpful in calculating the true wind speeds of the clouds, and give important clues about the composition and distribution of the interior. Once the interference from the solar wind and Enceladus are taken into account, the true rotation of Saturn can be determined precisely.

Then only one question remains: do they have commercials on Saturn FM?

Source: ESA News Release

Posted on by Nicholos Wethington

MIT Shoots For the Moon

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The Moon is a pretty popular destination these days: Google’s X-Prize is already getting applicants, Kaguya and Chang’e-1 are currently snapping pictures and taking measurements, and both India and the U.S. have missions lined up to launch in the next 10 years or so. MIT announced last week that it would join in on the fun, designing a spacecraft to study the Moon, schedule for launch in 2011.

In cooperation with NASA, MIT head a up a mission to send two satellites to simultaneously study the gravity field of the Moon in detail. Named GRAIL (Gravity Recovery and Interior Laboratory), the mission will study the gravity of the Moon to shed light on its thermal history and composition. By using two satellites to do so, GRAIL will create a map of the Moon’s gravity field that is 1,000 times more accurate than previous maps.

“After the three-month mission is completed, we will know the lunar gravitational field better than we know Earth’s,” said Maria Zuber, head of MIT’s Department of Earth, Atmospheric and Planetary Sciences, who will lead the mission.

GRAIL will use a similar method employed by GRACE (Gravity Recovery and Climate Experiment), a mission that has been mapping Earth’s gravitational field since 2002: two satellites constantly measure the distance between each other with great accuracy, thus creating a map as they orbit the Earth and travel through its gravity field.

GRACE uses GPS technology for the positioning of the satellites, something impossible to do on the Moon. Instead, the GRAIL satellites will precisely monitor radio signals coming from the Earth. This technology could also be used in future missions to other planets such as Mars and Venus.

Knowing the interior composition and history of the Moon will allow scientists to have a better understanding of the history of other planets in our Solar System. The evolution of the Moon, and the history of its many impact craters will help to create models for its formation, which serves as a record of planetary formation in the inner planets. Any future missions to land on the Moon could also benefit from extended mapping of the gravity field, as landers could use this data to prevent crashes and help navigate to the surface.

The mission will cost an estimated $375 million. The satellites will be constructed by Lockheed Martin Space Systems in Denver, Colo. and NASA’s Jet Propulsion Laboratory will develop the communication and navigation systems.

Original Source: MIT Press Release

Posted on by Nicholos Wethington

Cancer Rates Rise and Fall with Cosmic Rays

Showers of high energy particles occur when energetic cosmic rays strike the top of the Earth's atmosphere. Illustration Credit: Simon Swordy (U. Chicago), NASA.

Cancer is a mysterious and complicated disease, with many different types and causes. Researchers are still trying to track down all of the environmental effects that can lead to the disease, as anything from what someone eats to where they live determines the probability of developing cancer. A paper published in 2007 in the International Journal of Astrobiology looked at data for cancer deaths from around the world for the past 140 years, and found a strong correlation between rises in cancer deaths and the variation over time in the amount of galactic cosmic rays we encounter here on Earth.

In a paper titled, Correlation of a 140-year global time signature in cancer mortality birth cohorts with galactic cosmic ray variation by Dr. David A. Juckett from the Barros Research Institute at Michigan State University, he showed that the amount of deaths due to cancer on a global scale was higher when the background cosmic rays originating from outside the Solar System were more numerous.

The study looked at available cancer death data from the United States, United Kingdom, Australia, Canada and New Zealand for the past 100-140 years. These data were compared with the amount of variations in galactic cosmic rays during the same period, taken from analysis of ice core samples from Greenland and Antarctica.

Dr. Juckett showed that as the amount of cosmic ray activity increased, the number of people who died from cancer was also higher. There are two peaks in cosmic ray activity during this point, around 1800 and 1900, and a low point around 1860. The total deaths due to cancer were highest, though, around 1830 and 1930, and lowest in the 1890’s.

There is a 28-year lag between the increased presence of cosmic rays and the increase in cancer deaths. It’s not so simple as a person being exposed to cosmic rays and then developing cancer immediately afterwards. What is called the “grandmother effect” comes into play; the cosmic rays actually damage the germ cells of one’s parent while that parent is still in the grandmother’s womb.

“The grandmother would have to be exposed to radiation – which she is all the time – while she is pregnant with the mother of the affected individual. What this is basically implying is that, during a sensitive time in pregnancy, the constant background radiation may cause a chemical change in just the right cell and DNA stretch to lead to future cancer. The background radiation is causing very low level damage all the time to random cells in the body, but anything significant happening to germ cells would lead to a whole organism eventually carrying that damage (or predisposition),” said Dr. Juckett.

So, the parent is exposed to cosmic rays while the fetus is still developing, and this damage then emerges as cancer in child, but is not passed down further.

Galactic cosmic rays consist of high-energy radiation, and are composed primarily of high-energy protons and atomic nuclei. Their origin in not fully understood, but are thought to possibly come from supernovae, active galactic nuclei, quasars and/or gamma ray bursts.

There are several factors that may contribute to the flux of cosmic rays, and they may produce showers of secondary particles that penetrate and impact the Earth’s atmosphere and sometimes reach the surface.

In the study, the researchers found the trend between cosmic ray increase and cancer death increase was a global effect, but there are places on the Earth where the magnetosphere blocks more of the cosmic rays than others. At about 10°N of the equator, fewer cosmic rays get through than elsewhere on the Earth because of the way the Earth’s magnetosphere blocks energetic particles.

People in more northern and southern latitudes are exposed to more of this radiation, thus the rates of cancer death were higher in these regions than near the equator. On average, the oscillation in cancer deaths was between 10-15% during the period of the study.

Any good scientist will tell you that correlation does not necessarily mean causation; the increase in cosmic rays matches well the increase in cancer deaths over this time period, but there could yet be other reasons for this increase.

Dr. Juckett cautions, “Of course, other explanations could be hypothesized. Standard epidemiological approaches would partition individual cases by risk factors (e.g., smoking, environment pollution, diet, age-at-menarche, family history, etc.). Only when there is no correlation to these would other hypotheses, like cosmic rays be entertained. Unfortunately, to look at the 100-yr data for long-term trends, this kind of information is generally not available. The one thing that seems certain is that the common oscillations in the US, UK, CA, NZ, and AU data suggest a global environmental signal of some kind. This does limit things a bit (e.g., solar radiation effects, cosmic ray effects, global pollution).”

The effects that cosmic rays and other types of radiation have on human beings are important to study, as we venture outside the protective magnetic field of the Earth into space. The researchers said that “this effect has profound implications for evolution, long-distance space travel and the colonization of planets with high background radiation.” Long journeys in space would expose astronauts to this same type of radiation for long periods of time, so taking precautions to protect them makes good sense.

What can one do to protect themselves from this type of radiation here on Earth?

“I cannot of think of anything one can do to protect themselves from their inherited propensities. However, cancer is a multi-step process. It still requires other random ‘mutations’ to occur during life. Healthy living is still called for. In other words, reducing exposure to toxins, radiation, and injury. Eventually, the biochemical fingerprints of possible inherited changes may be deciphered and then testing could be possible,” said Dr. Juckett.

There is no cause for alarm, though; cosmic rays are only about 20-30% of the background radiation we are exposed to every day, and are a minimal cause of cancer in comparison to other environmental effects such as smoking.

Original Source: International Journal of Astrobiology

Posted on by Nicholos Wethington

Could We Detect Plants on other Planets?

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We’ve already found over 250 extrasolar planets, and more are continuing to be discovered fairly often. With all of these new planets popping up, the obvious question must be asked: how do we go about detecting whether or not they contain life? Though we can’t yet see features on the surface with even the most powerful of telescopes – and probably won’t be able to do so for a very long time – an analysis of the light coming from the planet may reveal if it is covered with life in the form of plants.

Dr. Luc Arnold of the CNRS Observatoire de Haute-Provence in France suggests that a spectral analysis of the light reflected off of a planet could determine whether or not it is covered with vegetation.

Earth’s plant-covered surface absorbs certain frequencies of light, and reflects others. Our vegetation has a very specific spectrum because it absorbs a lot of visible light around 700 nanometers, or the color we see as red. This is called the Vegetation Red Edge (VRE).

By looking at the sunlight that is reflected off of the Earth – Earthshine – the composition of the Earth’s surface and atmosphere can be determined. The Earth’s light can be analyzed when it is reflected off of the Moon, or from spacecraft distant enough from the Earth to see it as a small disk.

Knowing the composition of the Sun’s light, and adjusting for the elements and minerals in the atmosphere and on the surface, there is still between 0-10% of the photons near the red end of the visible spectrum that are missing. The factor needed to explain this photon absorption is the presence of plants, which use the light for photosynthesis

This same method could potentially be used to detect the presence of vegetation on extrasolar planets, proposes Dr. Arnold in a paper titled, Earthshine Observation of Vegetation and Implication for Life Detection on Other Planets published in the October 30th, 2007 edition of the journal Space Science Review.

“The point is that if, in the spectrum of an Earthlike planet, we find a spectral signature –probably different than the VRE – that cannot be explained as a mineral signature, nor an atmospheric signature, then the proposition that this feature is a possible signature of life becomes relevant. Especially if a variation in the strength of the signal is correlated with planet’s rotation period, suggesting that the spectral feature is on planet’s surface,” Dr. Arnold said.

The VRE on Earth is calculated by taking out “noise factors” such as the composition of the atmosphere, whether there are a lot of clouds, and whether the part of the Earth reflecting the light is covered by desert, ocean, or forest. All of these things absorb light in different parts of the spectrum. These same details must be sorted out for other planets to ensure that the absence of photons in a certain part of the spectrum is indeed due to plants absorbing the light.

To be able to rule out other factors in the spectrum of the planet, the resolution has to be better than is currently possible. ESA’s Darwin and NASA’s Terrestrial Planet Finder, both missions being designed to specifically look for new terrestrial planets and better study already-discovered ones, are expected to launch in the next 10 years or so. They will not be able to resolve the spectrum of extrasolar planets well enough to use this method for finding vegetation, but the second-generation of planet-finding telescopes will likely have this ability.

The question remains as to whether plants on distant worlds will use chlorophyll as their means of photosynthesizing light. Will the light they absorb be red, or a different color? Will the light they reflect be green or something completely bizarre, like magenta or bright blue? If they do use chlorophyll, their spectrum will be similar to that of our own planet. If not, their spectral signature may be rather different than that of Earth’s vegetation.

Dr. Arnold says a different VRE might still be rather interesting: “What would we say to us such a strange and different VRE ? It will reveal missing photons, i.e. photons form the star absorbed and ‘used’ (their energy) in an unknown or unidentified chemical process, that’s all we would learn. Here again, other information about the atmosphere composition (water vapor, oxygen, ozone, etc.) and temperature would help to make coherent proposals. At least it would feed an very exciting debate!”

Source: Space Science Review

Posted on by Nicholos Wethington

Europa’s Ocean: Thick or Thin?

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How do you determine the thickness of an ocean that you can’t see, let alone know how salty it is? Europa, the sixth satellite from Jupiter, is thought to have an ocean of liquid water underneath its icy surface. We know this because of its remarkably uncratered surface and the way its magnetic field reacts with that of Jupiter. New results that take into consideration Europa’s interaction with the plasma surrounding Jupiter – in addition to the magnetic field – give us a better picture of the ocean’s thickness and composition. This will help future robotic explorers know how deep they need to tunnel to reach the oceans underneath.

“We know from gravity measurements made by Galileo that Europa is a differentiated body. The most plausible models of Europa’s interior have an H2O-ice layer of thickness 80-170km. However, the gravity measurements tell us nothing about the state of this layer (solid or liquid),” said Dr. Nico Schilling of the Institut für Geophysik und Meteorologie in Köln, Germany.

The water in Europa’s ocean – just like the water in our own ocean – is a good conductor of electricity. When a conductor passes through a magnetic field, electricity is produced, and this electricity has an effect on the magnetic field itself. It’s just like what happens inside an electric generator. This process is called electromagnetic induction, and the intensity of the induction gives a lot of information about the materials involved in the process.

But Europa doesn’t only interact with the magnetic field coming from Jupiter, however; it also has electromagnetic interactions with the plasma surrounding Jupiter, called the magnetospheric plasma. This same thing happens on Earth in a way that is very familiar: Earth has a magnetosphere, and when plasma coming from the Sun interacts with our magnetosphere we see the beautiful Aurora Borealis phenomenon.

This process, happening intermittently as Europa orbits Jupiter, has an effect on the induction field of the subsurface ocean of the moon. By combining these measurements with the previous measurements of the interaction between Europa and Jupiter’s magnetic field, the researchers were able to get a better picture of just how thick and how conductive Europa’s ocean is. Their results were published in a paper titled, Time-varying interaction of Europa with the jovian magnetosphere: Constraints on the conductivity of Europa’s subsurface ocean, which appears in the August 2007 edition of the journal Icarus.

The researchers compared their models of Europa’s electromagnetic induction with the results of Galileo’s magnetic field measurements, and found that the total conductivity of the ocean was about 50,000 Siemens (a measure of electrical conductivity). This is much higher than previous results, which placed the conductivity at 15000 Siemens.

Depending on the composition of the ocean, though, the thickness could be between 25 and 100km, which is also thicker than the previously estimated lower limit of 5km. The less conductive the ocean is, the thicker it must be to account for the measured conductivity, and this depends on the quantity and type of salt found in the ocean, which still remains unknown.

Taking into account the interactions with the magnetospheric plasma are important when studying the composition of planets and moons.

Dr. Schilling said, “The plasma interaction effects the magnetic field measurements, but not e.g. the gravity measurements. So in every case in the Jupiter system, where magnetic field measurements were used to get some informations from the interiors of the moons, the plasma interaction has to be considered. An example is for instance Io, where the first flybys suggested that Io may have an internal dynamo field. It turned out that the measured magnetic field perturbation was not an internal field but was created by the plasma interaction.”

Europa and Io, though, are not the only place where magnetic fields and plasma interactions can tell us about the nature of a planet’s interior; this same method was also used to detect the geysers of Enceladus, one of Saturn’s moons.

“The first hints of an active south polar region came from the magnetic field measurements and the simulations of the plasma interaction, before Cassini actually saw the geysers,” Dr. Schilling said.

With the discovery of entire ecosystems at the bottom of oceans here on Earth – ecosystems entirely cut off from sunlight – the discovery of oceans on Europa gives scientists hope that there could be life there. And this new discovery helps researchers understand what kind of ocean they could be dealing with.

Now, we just have to tunnel down through the shell of ice and look for ourselves.

Source: Icarus

Posted on by Nicholos Wethington

Future Mars Explorers Might Only See the Planet from Orbit

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When the first humans travel to Mars, the journey will be dangerous. Perhaps the most dangerous part will be the landing; the thin Martian atmosphere makes it extremely difficult to slow down a heavy spacecraft carrying humans. To minimize the danger, the first missions to Mars might not have people land on the surface at all. Instead, they might orbit the Red Planet, and control virtual robots working down below. Just imagine how much science Martian rovers controlled by humans could get done, all from the safety of orbit – at a fraction of the cost of actually setting foot on the planet.

“It is a cheaper, simpler, and safer way to explore, and hence it will be a faster way to explore. Virtual exploration will have the excitement of being there, at a fraction of the price, ” Dr. Landis wrote in a paper titled, Teleoperation from Mars orbit: A proposal for human exploration, published in the May 2007 issue of Acta Astronautica.

A mission to Mars using teleoperation would involve robots landed on the surface which would be controlled directly by astronauts in a spacecraft orbiting the planet. The robots would be more sophisticated than current rovers, with hands and bodies that would mimic the movements of a human being, thus allowing the operator to control the robot using a virtual reality interface. The current lag between the commands from the Earth and their reception by the rovers on Mars can be several minutes, but an orbiter controlling the robots would experience almost no delay at all.

Unlike humans, the Robonauts wouldn’t need a habitat on the surface, and could be left there. They could also be equipped with a large variety of scientific equipment, and wouldn’t need to rest, making the exploration of the surface faster and more efficient.

Sure, it seems a little silly to send humans all the way out to Mars without actually landing them on the surface, but doing so poses many challenges that are eliminated by a teleoperation mission. To design and provide fuel for a vehicle to land on the surface, and then take off, is very expensive both in terms of weight and money.

We still don’t know if there is life on the surface of Mars, so being very careful not to contaminate the surface with Earth microbes is also important. Any missions that land on the surface have the potential of leaving life from our own planet there, making it difficult to later determine the origin of life on Mars – if any exists – and Earth microbes could possibly wipe out any Martian life.

Also, the effect potential life on Mars could have on human beings is unknown, so it is better to be safe than risk the lives of astronauts through exposure to possibly harmful alien life.

Teleoperated missions would expand the areas of Mars that could be explored, since the issue of safety is not as much of concern when using robots.

“Landing sites for a human mission are likely to be scientifically “boring” sites, featuring flat surfaces with an absence of boulders, cliffs, channels, craters or mountains. Use of telerobots lowers risk, and thereby allows dangerous exploration,” Dr. Landis wrote.

Teleoperation wouldn’t be the end, of Mars exploration, though; it’s merely a step towards landing humans on the planet to ensure the safety of astronauts and gain better information on how to conduct future missions.

Source: Acta Astronautica

Posted on by Nicholos Wethington

How Old is Triton’s Surface?

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With all of the press going to the moons of Jupiter and Saturn, it’s about time that Neptune got a turn. Triton, one of the moons of Neptune, is curious, with large swaths of the planet resembling the skin of a cantaloupe and a retrograde orbit (opposite that of Neptune’s rotation). Its surface is thought to be rather young, and a new method of counting the craters that pock the moon may push the age of Triton’s surface back even younger than previously thought.

Dr. Paul Schenk of the Lunar and Planetary Institute in Houston, and Kevin Zahnle of the NASA Ames Research Center in California revisited the pictures of Triton’s surface that the Voyager 2 spacecraft took in 1989. By clarifying the images with current technology, they were able to count with very high accuracy the amount of craters, and determine the possible causes of the craters. Their results were published in the July 2007 issue of the journal Icarus, in a paper titled On the negligible age of the surface of Triton.

“Our new crater counts benefit from several improvements in the quality of the Voyager images. Although this does not make invisible craters visible, it does increase the ability to discriminate impact features on Triton,” the researchers wrote.

The images showed that the leading hemisphere — the hemisphere of the planet in the direction of its orbit around Neptune — contains many more craters than that of the trailing hemisphere. Triton is tidally locked to Neptune, which means that – like our Moon – an observer on Neptune would always see the same face of Triton. Thus, the same hemisphere would always face the direction of Triton’s orbit around Neptune.

The researchers propose, “Our map of craters on Triton indicates that all definitive impact craters are on the leading hemisphere. The apparent cratering asymmetry of Triton is extreme. The absence of craters on the trailing hemisphere, and the low frequency of craters near the boundary between leading and trailing hemispheres is unique in the Solar System.”

Since Triton is rotating in the opposite direction of everything else that goes around Neptune, it acts like a giant “vacuum cleaner,” and picks up any debris orbiting the planet in a prograde (the same as Neptune’s rotation) direction.

Triton is thought to have given itself a makeover very recently because it was captured by Neptune long ago; most likely, Triton was one body in a binary system, and when Neptune captured it, the other body was thrown out of the Solar System. After being captured, all of the energy that went into slowing Triton down into orbit around Neptune was transferred into heat that melted the surface and interior of the planet. This heat could have lasted for millions of years, and the tidal energy from Neptune may still warm the interior of Triton today.

Normally, areas that have less craters have been resurfaced more recently, and thus are generally younger than surfaces with lots of craters. By analyzing the density of the craters, and using information about the type and frequency of debris that possibly caused them, the researchers were able to calculate that the terrain on the trailing hemisphere with less craters than that of the leading hemisphere was actually older than the area with more craters.

“Whatever their origin, the paucity of impact craters (and heliocentric craters in particular) suggests that Triton’s surface is very young, younger than 100 million years and possibly as young as a few million years. A return to Neptune and its vigorous, dynamic moon Triton is long overdue,” the researchers wrote.

Source: Icarus