Mars

Mars - The Red Planet

Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color; Mars is sometimes referred to as the Red Planet. (An interesting side note: the Roman god Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing and terraforming Mars may prefer this symbolism.) The name of the month March derives from Mars.

Mars has been known since prehistoric times. Of course, it has been extensively studied with ground-based observatories. But even very large telescopes find Mars a difficult target, it's just too small. It is still a favorite of science fiction writers as the most favorable place in the Solar System (other than Earth!) for human habitation. But the famous "canals" "seen" by Lowell and others were, unfortunately, just as imaginary as Barsoomian princesses.

The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 1997 July 4. In 2004 the Mars Expedition Rovers "Spirit" and "Opportunity" landed on Mars sending back geologic data and many pictures; they are still operating after more than three years on Mars. In 2008, Phoenix landed in the northern plains to search for water. Three Mars orbiters (Mars Reconnaissance Orbiter, Mars Odyssey, and Mars Express) are also currently in operation.

Mars' orbit is significantly elliptical. One result of this is a temperature variation of about 30 C at the subsolar point between aphelion and perihelion. This has a major influence on Mars' climate. While the average temperature on Mars is about 218 K (-55 C, -67 F), Martian surface temperatures range widely from as little as 140 K (-133 C, -207 F) at the winter pole to almost 300 K (27 C, 80 F) on the day side during summer.

Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.

Mars has some of the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular:

Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.

Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.

Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep (top of page);

Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.

Much of the Martian surface is very old and cratered, but there are also much younger rift valleys, ridges, hills and plains. (None of this is visible in any detail with a telescope, even the Hubble Space Telescope; all this information comes from the spacecraft that we've sent to Mars.)


The southern hemisphere of Mars is predominantly ancient cratered highlands somewhat similar to the Moon. In contrast, most of the northern hemisphere consists of plains which are much younger, lower in elevation and have a much more complex history. An abrupt elevation change of several kilometers seems to occur at the boundary. The reasons for this global dichotomy and abrupt boundary are unknown (some speculate that they are due to a very large impact shortly after Mars' accretion). Mars Global Surveyor has produced a nice 3D map of Mars that clearly shows these features.

The interior of Mars is known only by inference from data about the surface and the bulk statistics of the planet. The most likely scenario is a dense core about 1700 km in radius, a molten rocky mantle somewhat denser than the Earth's and a thin crust. Data from Mars Global Surveyor indicates that Mars' crust is about 80 km thick in the southern hemisphere but only about 35 km thick in the north. Mars' relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of sulfur in addition to iron (iron and iron sulfide).



Recent observations with the Hubble Space Telescope have revealed that the conditions during the Viking missions may not have been typical. Mars' atmosphere now seems to be both colder and dryer than measured by the Viking landers (more details from STScI).


The Viking landers performed experiments to determine the existence of life on Mars. The results were somewhat ambiguous but most scientists now believe that they show no evidence for life on Mars (there is still some controversy, however). Optimists point out that only two tiny samples were measured and not from the most favorable locations. More experiments will be done by future missions to Mars.

A small number of meteorites (the SNC meteorites) are believed to have originated on Mars.

When it is in the nighttime sky, Mars is easily visible with the unaided eye. Mars is a difficult but rewarding target for an amateur telescope though only for the three or four months each martian year when it is closest to Earth. Its apparent size and brightness varies greatly according to its relative position to the Earth. There are several Web sites that show the current position of Mars (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.
 
 
 

A satellite photo shows the "face" on Mars, one of several of the planet's volcanic surface features.

In addition to volcanoes, another amazing geological feature in the Tharsis area of Mars is a massive canyon system known as Valles Marineris. This geological wonder was formed billions of years ago when pressure within the planet's interior caused the crust to swell and split open, creating immense gashes in the surface. The canyon system is three thousand miles long, five miles deep, and in some places more than four hundred miles wide. If Valles Marineris were on Earth, it would stretch across the entire United States and make the Grand Canyon look like nothing more than a tiny crevice in the ground.

Mystery image of 'life on Mars'

That's a headline of a recent article on BBC News covering this early image from the Spirit rover.

An image of a mysterious shape on the surface of Mars, taken by Nasa spacecraft Spirit, has reignited the debate about life on the Red Planet.

A magnified version of the picture, posted on the internet, appears to some to show what resembles a human form among a crop of rocks.

It goes on to say...

When the robotic rover set down on 24 January 2004, its images disappointed space-watchers hoping for signs of extraterrestrial life.


Now they appear convinced that this image provides the evidence they have been trawling Nasa's photo files for.

The blown-up image seems to resemble a figure striding among the Martian rocks.

The internet has been abuzz with postings offering theories.

One said it was a garden gnome, another that it was the Virgin Mary.

A third suggested Bigfoot, the hairy bipedal mountain beast that appears in various guises in a number of legends around the world.

But the consensus seemed to be that it bore a striking resemblance to the Little Mermaid statue in the Danish capital, Copenhagen.

Saturn, Uranus and Neptune

Saturn

Naked Saturn

Here's one of the first raw images of Saturn taken by the Cassini spacecraft just after equinox, on August 12, 2009. The planet sure looks naked without its rings! But not to fear, the rings are still there; we just can't see them very well — only a thin line. That's because the sun was shining directly straight-on at the rings at Saturn's equinox, and the spacecraft was in the right place, too. Equinox occurs every half-Saturn-year which is equivalent to about 15 Earth years. The illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures and some moons to cast long shadows across the rings. The ring shadows themselves have become a rapidly narrowing band cast onto the planet. Below, see another image with the rings visible as the spacecraft changed its angle.

Saturn's rings at equinox. Credit: NASA

Mystery Object Pierces a Saturn's Ring

August 11, 2009—A mystery object that punched through one of Saturn's thin outer rings created a glittering spray of ice crystals and pulled some material along in its wake, as seen in this rare image recently released by NASA's Cassini orbiter.

The puncture, which Cassini snapped on June 11, is among the many marvels that have been revealed in the weeks leading up to Saturn's equinox, which happens today. (Find out how the equinox has helped astronomers find new moons, how it will make Saturn temporarily "lose" its rings, and more.)
Equinoxes occur at the point in a planet's orbit when the sun shines directly on the planet's equator. Earth has two equinoxes each year, one in spring and another in autumn. (See an equinox video.)
Because of Saturn's comparatively long orbit around the sun, the ringed planet has an equinox just once every 15 Earth years.
This celestial alignment lowers the angle at which sunlight strikes Saturn, causing objects higher or lower than the ring plane to cast long shadows—and offering scientists a completely new look at the gas giant and its rings.

"We're finally seeing the rings in three dimensions," said Carolyn Porco of the Space Science Institute in Boulder, Colorado. "This is the fist time in history that we've been there watching as this happens."

The object is most likely a small satellite, or moonlet, that is zipping around Saturn on an inclined orbit, said Porco, who leads Cassini's imaging team.
The moonlet appears to be about 0.6 mile (a kilometer) wide, but a comet-like haze of ice crystals and dust surrounding it may be obscuring its true size, Porco added.

Scientists think Saturn's moonlets are fragments of larger moons that were shattered by asteroids or comets eons ago.
It's possible that the object is a small comet or asteroid barreling through the ring, said Nicole Albers, a Saturn-ring scientist at the University of Colorado at Boulder. But such occurrences are rare.

"Since we suspect that there are moonlets in the F ring," Albers said, "it's really not unlikely that it is one."

 
 
Temporary Radiation Belt Discovered at Saturn
 
 

A new, temporary radiation belt has been detected at Saturn, located about 377,000 km from the center of the planet , near the orbit of the moon Dione. The temporary radiation belt was short-lived and formed three times in 2005. It was observed as sudden increases in the intensity of high energy charged particles in the inner part of Saturn's magnetosphere, in the vicinity of the moons Dione and Tethys, and likely was caused by a change in the intensities of cosmic rays at Saturn.

"These intensifications, which could create temporary satellite atmospheres around these moons," said Dr. Elias Roussos, "occurred three times in 2005 as a response to an equal number of solar storms that hit Saturn's magnetosphere and formed a new, temporary component to Saturn’s radiation belts.”

The discovery was made possible by Cassini's five-plus year mission, allowing scientists to observe and assess changes in Saturn's radiation belts. An international team of astronomers made the discovery analyzing data from the Magnetospheric Imaging instrument (MIMI) on Cassini MIMI’s LEMMS sensor, which measures the energy and angular distribution of charged particles in the magnetic bubble that surrounds Saturn.

The new belt, which has been named “the Dione belt”, was only detected by MIMI/LEMMS for a few weeks after each of its three appearances. The team believe that newly formed charged particles in the Dione belt were gradually absorbed by Dione itself and another nearby moon, named Tethys, which lies slightly closer to Saturn at an orbit of 295 000km.


Unlike the Van Allen belts around the Earth, Saturn’s radiation belts inside the orbit of Tethys are very stable, showing negligible response to solar storm occurrences and no variability over the five years that they have been monitored by Cassini.

Interestingly, it was found that the transient Dione belt was only detected outside the orbit of Tethys. It appeared to be clearly separated from the inner belts by a permanent radiation gap all along the orbit of Tethys.

“Our observations suggest that Tethys acts as a barrier against inward transport of energetic particles and is shielding the planet’s inner radiation belts from solar wind influences. That makes the inner, ionic radiation belts of Saturn the most isolated magnetospheric structure in our solar system“, said Dr Roussos.

The radiation belts within Tethys's orbit probably arise from the interaction of the planet’s main rings and atmosphere and galactic cosmic ray particles that, unlike the solar wind, have the very high energies needed to penetrate the innermost Saturnian magnetosphere. This means that the inner radiation belts will only vary if the cosmic ray intensities at the distance of Saturn change significantly.

However, Roussos emphasized that outside the orbit of Tethys, the variability of Saturn's radiation belt might be enhanced in the coming years as solar maximum approaches. "If solar storms occur frequently in the new solar cycle, the Dione belt might become a permanent, although highly variable, component of Saturn's magnetosphere, which could affect significantly Saturn's global magnetospheric dynamics,” he said.

The new findings were presented at the European Planetary Science Congress in Potsdam, Germany.
http://www.nancyatkinson.com/

Uranus

Uranus is much smaller than Jupiter and Saturn, but with a diameter of 51,118 km, it is still over four times that of Earths. It would take 15 of our planet to equal the mass of Uranus.

Though Uranus is the next planet out from Saturn, it is over twice Saturn's distance from the Sun. Being 28.69 x 108 km from the Sun, Uranus is a cold world with an average temperature of -221 C above cloud tops. And clouds are all we have ssen of this distant cold world. Even the Voyager spacecraft could not see beyond those clouds.

Uranus was not known to the ancient astronomers who knew only those planets out to Saturn. Uranus was too distant to be seen with the unaided eye. This planet had to wait until 1781 when the astronomer William Herschel discovered it while hunting for comets.

Neptune

Neptune is a big world, about 49,530 km in diameter, but despite being sometimes referred to as a lesser gas-giant, it’s not a colossus like Jupiter. It’s not even mostly gas. The sphere we see from outside is only the top of a deep, thick atmosphere. About 20% of Neptune’s apparent diameter is air, mostly hydrogen and helium, but with a fair tincture of methane and ammonia, and some more complex organics at trace levels. As one dives into Neptune the outer air starts off very cold. The planet is 30 AU from the Sun, after all. But inside Neptune the heat rises with depth… along with pressure. At a depth where the air is about as dense as what you’re breathing, the temperature is about -200° C, or ~70 Kelvins… but by the time things warm up to room temperature – around 300 Kelvins – you’d be crushed by over 50 atmospheres of pressure. One of those deep-diving suits from the old movies would be required to survive (along with oxygen tanks, of course).

Below that, things get weird. I said there’s no ocean on Neptune, but there is something like an ocean. As pressure climbs during your dive into Neptune, the atmosphere would gradually thicken into something very much like a liquid. True liquid water can’t exist anywhere inside Neptune, because there is too much hydrogen. The hydrogen molecules shove their way in amongst individual water molecules so much that water can’t fully condense into a true liquid. But at the crushing pressures of Neptune’s interior the thick, hot H2O, H2 and He gas compresses to water-like densities… except it’s not liquid water, and the temperature is over 2000° C. Those temperatures are hot enough to melt iron, and are far too hot for any organic compounds to survive. It is decidedly not an abode for life (as we know it, I must add with geeky circumspection).

But what if all that dense quasi-fluid were cooler? Neptune generates 2.6 times more energy in its core than it receives from the Sun, mostly from radioactive decay in its rocky heart. Really, “core” is an odd word to use, because this rocky kernel is more massive than four Earths. For all we know it might have an adorable little metallic iron core all its own, about the size of ours. In any event, heat from below combined with the thin solar light at 30 AU keep Neptune’s water from condensing as rain. But… if Neptune were colder at its cloud tops, and cooler within, its water could drop out to form a massive ocean realm.

What would such a realm be like? Half the planet’s apparent diameter is currently a hot, ionic quasi-liquid right now, but cooled that material would condense into an ocean thousands of kilometers deep. As a comparison, the Mariana Trench is the deepest part of our ocean, at 10 km. Neptune’s ocean would be hundreds of times deeper, and much stranger. If Neptune had a water ocean, its floor wouldn’t be rock, it would be solid ice. Heavy ice… ice VII, or X, or XI, or some other weird crystalline water-lattice that can survive at ten million atmospheres of pressure. Heat would rise from below, from the imprisoned mass of searing rock in Neptune’s center. Volcanic heat from the core mass would bubble up, melting the icy oceanic crust, and inseminating the deep ocean with precious minerals. Could life exist in such an alien environment?

Maybe. If Neptune could cool enough that it supports a liquid ocean, it might also give birth to life. Only when its massive, world-girdling ocean cools to become normal water, instead of a seething ionic mantle, will the conditions be even remotely similar to what conventional life requires. The big question, of course, is… can that happen?

The answer appears to be a qualified yes. Eventually, when its interior furnaces wind down a bit, and its atmosphere can cool enough, seas become possible on Neptune. The only problem… and it’s a fairly big problem, from our perspective… is that before that can happen the Sun has to go away. Specifically, the Sun must live out its long, long life and ultimately wither into a fading white dwarf. The post-solar white dwarf must, in turn, fade from blazing incandescence to a dim sputter. At that point, tens of billions of years from now, Neptune will cool enough to bear oceans. But not until.

There are two ways of looking at this news. From a purely selfish point of view, I’m quite cross that I’ll never be able to see what titans of the deep Neptune’s olympian waters might birth. But from a larger perspective I’m encouraged. Even when the Sun goes dark, it will be possible for life to spawn… or transplant itself and survive… in our solar system. The details will differ from what we’re familiar with today, on Earth, but water in the dim astronomical future will still require fins, and streamlining, to move through, and the animals of any Neptunian ocean of 100 billion years from now will still need to be sleek and smooth and tapered. I don’t have to see them for myself, because I can use chemistry, thermodynamics, geology, and physics to construct a probabilistic prognostication. Or two, or ten… There are many ways the future of Neptune may work out, but among them are highly realistic ways that lead to life, and complexity, and possibly thought… in a future so deep our own biosphere will be an impossibly ancient memory from a time older than the Big Bang is to us.

When will Neptune get oceans?
 
Yes, and a strange question that is. But actually not an unrealistic question. Neptune, now the farthest true planet from the Sun (after Pluto’s demotion), is namesake to the ancient god of the oceans. Neptune is shrouded in layers of icy, dense air laced with enough methane to color the world azure blue… hence the world’s maritime label. But despite its pelagic associations, Neptune has no oceans… though it might have had, with a slightly different composition. And it’s very possible that Neptune will one day be covered in a deep, wine-black sea of cool, liquid water.

Pluto, Mercury and Venus

Pluto

Why pluto is not a planet anymore?

Pluto has been voted off the island.

The distant, ice-covered world is no longer a true planet, according to a new definition of the term voted on by scientists today.

"Whoa! Pluto's dead," said astronomer Mike Brown, of the California Institute of Technology in Pasadena, as he watched a Webcast of the vote. "There are finally, officially, eight planets in the solar system."


In a move that's already generating controversy and will force textbooks to be rewritten, Pluto will now be dubbed a dwarf planet.

But it's no longer part of an exclusive club, since there are more than 40 of these dwarfs, including the large asteroid Ceres and 2003 UB313, nicknamed Xena—a distant object slightly larger than Pluto discovered by Brown last year.

"We know of 44" dwarf planets so far, Brown said. "We will find hundreds. It's a very huge category."

A clear majority of researchers voted for the new definition at a meeting of the International Astronomical Union (IAU) in Prague, in the Czech Republic. The IAU decides the official names of all celestial bodies.

The tough decision comes after a multiyear search for a scientific definition of the word "planet." The term never had an official meaning before.


What Is a Planet Today?

According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.

Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.

Mercury

Mercury, the closest planet to the Sun, remains the most mysterious of the Solar System's inner planets. Hiding in the Sun's glare it is a difficult target for Earth bound observers. The only spacecraft to explore Mercury close-up was Mariner 10 which executed 3 flybys of Mercury in 1974 and 1975, surveying approximately 45 percent of its surface. Mariner 10 deftly manuevered to photograph part of the sunlit hemisphere during each approach, passed behind the planet, and continued to image the sun-facing side as the spacecraft receded. Its highest resolution photographs recorded features approximately a mile across. A recent reprocessing of the Mariner 10 data has resulted in this dramatic mosaic. Like the Earth's Moon, Mercury's surface shows the scars of impact cratering - the smooth vertical band and patches visible above represent regions where no image information is available.

Venus

The Brightest Planet

Venus and Earth are similar in size, mass, density, composition, and distance from the sun. There, however, is where the similarities end.

Venus is covered by a thick, rapidly spinning atmosphere, creating a scorched world with temperatures hot enough to melt lead and a surface pressure 90 times that of Earth. Because of its proximity to Earth and the way its clouds reflect sunlight, Venus appears to be the brightest planet in the sky.

Like Mercury, Venus can be seen periodically passing across the face of the sun. These transits occur in pairs, with more than a century separating each pair. Since the telescope was invented, transits have been observed in 1631, 1639; 1761, 1769; and 1874, 1882. On June 8, 2004, astronomers worldwide saw the tiny dot of Venus crawl across the sun; the second in this pair of early 21st-century transits will occur June 6, 2012.


Toxic Atmosphere

Venus's atmosphere consists mainly of carbon dioxide, with clouds of sulfuric acid droplets. Only trace amounts of water have been detected in the atmosphere. The thick atmosphere traps the sun's heat, resulting in surface temperatures over 880 degrees Fahrenheit (470 degrees Celsius). Probes that have landed on Venus have not survived more than a few hours before being destroyed by the incredibly high temperatures.

The Venusian year (orbital period) is about 225 Earth days long, while the planet's rotation period is 243 Earth days, making a Venus day about 117 Earth days long. Venus rotates retrograde (east to west) compared with Earth's prograde (west to east) rotation. Seen from Venus, the sun would rise in the west and set in the east. As Venus moves forward in its solar orbit while slowly rotating "backwards" on its axis, the cloud-level atmosphere zips around the planet in the opposite direction from the rotation every four Earth days, driven by constant hurricane-force winds. How this atmospheric "super rotation" forms and is maintained continues to be a topic of scientific investigation.

About 90 percent of the surface of Venus appears to be recently solidified basalt lava; it is thought that the planet was completely resurfaced by volcanic activity 300 million to 500 million years ago.

Sulfur compounds, possibly attributable to volcanic activity, are abundant in Venus's clouds. The corrosive chemistry and dense, moving atmosphere cause significant surface weathering and erosion. Radar images of the surface show wind streaks and sand dunes. Craters smaller than 0.9 to 1.2 miles (1.5 to 2 kilometers) across do not exist on Venus, because small meteors burn up in the dense atmosphere before they can reach the surface.


Geological Features

More than a thousand volcanoes or volcanic centers larger than 12 miles (20 kilometers) in diameter dot the surface of Venus. Volcanic flows have produced long, sinuous channels extending for hundreds of kilometers.

Venus has two large highland areas: Ishtar Terra, about the size of Australia, in the north polar region, and Aphrodite Terra, about the size of South America, straddling the equator and extending for almost 6,000 miles (10,000 kilometers). Maxwell Montes, the highest mountain on Venus and comparable to Mount Everest on Earth, is at the eastern edge of Ishtar Terra.

Venus has an iron core about 1,200 miles (3,000 kilometers) in radius. Venus has no global magnetic field; though its core iron content is similar to that of Earth, Venus rotates too slowly to generate the type of magnetic field that Earth has.