The good news:
The bad news:
Occasionally, Mars whitnesses giant sand storms which enshroud the entire planet in dust. The thin atmosphere of Mars prohibits strong wind forces even when the wind speeds get very high by Earth standards. NASA's Hubble Space telescope whitnessed a giant dust storm on Mars in 2001.
And for fun:
If your weight on Earth is 75kg, your weight on Mars will be 28.4kg because the gravity of Mars is 0.379 of Earth's. On the other hand, suppose you are 50 earth years old, you would be 26 if you were a Martian. That is because a year on Mars is 1.881 times longer than on Earth.
What do the constellations look like on Mars? Would we see our famous Orion and the summer triangle or would we see different figures? No doubt, it would be exciting to see new constellations, however, they are exactly the same. Mars is our neighbor planet in a distance varying between 0.36 and 2.68 average earth-sun distances (AU). The stars lie in distances we use to measure in light-years. The relatively small step to Mars does not make any difference in angular star positions. Even as seen from Pluto, the constellations will still look as if we observed them from Earth.
Due to Mars' different inclination of its equator to its orbit and its orbit to the ecliptic, the north celestrial pole star is not Polaris but near Deneb (Alpha Cygnus) and Alpha Cephei while the brightest star (magnitude 1.9) near the southern pole is delta Velorum, yet well 3° away from the south celestrial pole.
Consequently, Mars has no exact pole stars (just like Earth). The coordinates for 1 January 2000 are R.A. 21h10m43" and declination 52°53"09" for the north pole and 9h10m43" (north pole minus 12 hours) and -52°53"09" for the south pole. Just like the tips of the Earth axis wobble as a result of precession and nutation, so does the axis of Mars, in that the exact polar celestial coordinates change slightly over time. The small moons of Mars have no stabilizing effect on Mars in that the variation of Mars"s axial tilt is much larger than for Earth.
Inspite of the unchanged constellations, a Mars observatory will see a few significant changes. These include the close asteroid-like moons of Mars, the bright inner "double-planet" Earth as a morning or evening star, the smaller size of the Sun, the different sizes and brightnesses of the other planets, the much closer dwarf planet Ceres, asteroid Vesta, appearance of meteors, cosmic rays and more.
Researchers used the left eye camera of Curiosity's Mast Camera (Mastcam) to capture this scene about 80 minutes after sunset on the 529th Martian day, or sol, of the rover's work on Mars (Jan. 31, 2014). The image has been processed to remove effects of cosmic rays. The Earth and Moon dots have been brightened up to about twice the brightness recorded by the camera. A human observer with normal vision, if standing on Mars, could easily see Earth and the moon as two distinct, bright "evening stars." The distance between Earth and Mars when Curiosity took the photo was about 99 million miles (160 million kilometers).
Most apparently, there is no large, bright moon like ours. Mars has two natural satellites, the inner moon Phobos (Greek for 'fear') and the outer moon Deimos (Greek for 'panic'). Both are not round like our moon. They look more like asteroids or oblong, potato shaped rocks that may have been snared by Mars' gravity now performing as moons. Phobos lies 9,400km away from Mars' center while Deimos is 23,500km away. Since the eccentricity of Deimos is zero, it orbits at an almost constant distance and velocity. Phobos' eccentricity is comparable to that of Earth nearing Mars at a rate of 1.8 meters every hundred years; at that rate, in 50 million years, it will either crash into Mars or break up into a ring.Left: View onto North of the orbits of the martian moons drawn to scale. The sizes of the moons are much exaggerated. ex is the orbit eccentricity, i the orbit inclination to Mars's equator. The distance from the core of Mars is given in Mars radii.
Phobos orbits Mars three times a day (once in 0.32 earth days) in a low-inclination equatorial orbit and is so close to the planet's surface that it cannot be seen in locations on Mars over 70° northern or southern latitudes. The moon rises in the west and sets in the east (reverse apparent motion) because it orbits Mars three times faster than the planet rotates around its axis. The time between two meridian transits is about 11.11 hours while the duration of visibility lasts 4.24 hours on the equator and over 5 hours on ±65° latitudes. Phobos rotates around its axis in the same time as it orbits Mars. The moon is therefore tidally locked and shows Mars always the same face, just like our Moon and many other planetary moons.
Given its size (27 by 22 by 18 km) and distance to Mars' surface (5980 km on the equator), Phobos apparent size is 1/2 of the moon across its longest axis, large enough to spot its most significant impact crater known as "Stickney" with the unaided eye. Due to the additional distance observers on higher latitudes will see a smaller moon. Actually, due to its close proximity to Mars' surface, Phobos' apparent size varies by up to 45%! The apparent visual magnitude is around -9mv, 1/30 as bright as our full moon.
Just like our Moon casts a shadow during a solor eclipse the penumbral shadow of Phobos during a Martin eclipse has been photographed by the Mars Global Surveyor on August 26, 1999 as it cast upon western Xanthe Terra at about 2 p.m. local time on Mars. The image covers an area about 250 kilometers (155 miles) across and is illuminated from the left.
As seen from Mars, the outer moon Deimos appears between 1.8 and 2.6 arc minutes wide because it lies further out 20,060 km from the surface on the equator and is smaller than Phobos, namely 15 by 12 by 11 km across. It circles Mars in 30.3 hours and shines at maximum -5.5 visual magnitude, brighter than Venus.
Because it exceeds the martian rotation of 24.6 hours, Deimos rises in the east and sets in the west. It transits the meridian every 131 hours (5.5 days) while it takes 59.5 hours (2.5 days) between rising and setting on the equator or 64.6 hours (2.7 days) at 80° northern or southern latitides. Although over 3 times further out than Phobos, Deimos cannot be observed at martian latitudes higher than ±82 degrees. Interestingly, Deimos is tidally locked to Mars as Phobos is.
This image shows the passing, or transit, of the martian moon Deimos over the Sun. Taken by Mars Exploration Rover Opportunity on sol 39 of its mission. NASA/JPL/Cornell.
This movie clip shows the larger of Mars' two moons, Phobos, passing in front of the smaller Martian moon, Deimos, as observed by NASA's Mars rover Curiosity. The series of 41 images is shown at increased speed. The actual elapsed time is 55 seconds. The images were taken by the telephoto-lens camera of the Mast Camera pair (right Mastcam) on Curiosity on Aug. 1, 2013, during the 351st Martian day, or sol, of Curiosity's work on Mars. These observations of Phobos and Deimos help researchers make knowledge of the moons' orbits even more precise. On Phobos, Stickney Crater is visible on the bottom. It is on the leading hemisphere of Phobos. Hall Crater, in the south, is the prominent feature on the right hand side.
Image Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.
Depending on a moon's orbit position relative to an observer the distance and therefore the angular sizes during a moon orbit period varies. The illustration shows the observer on the equator of Mars, however, when moving to higher latitudes the distances grow further as a result of the additional angular distance from the equator.This illustration demonstrates the effect of the observer's latitude. This phenomena is common to all moons in the solar system, however, it is more apparent with closely orbiting moons.
Let's create a model shrinking Mars and its tiny moons to a far smaller scale. If Mars were the size of a basketball (25 cm or 10 inches) in diameter, Phobos would be a grain 1mm across and 34.5cm away from the basketball (Mars), while Deimos measures 0.55mm and is 86.3cm away. Probably it would be hard to pinpoint the moons. In true space, other "grains" are much farther away while Phobos and Deimos are the brightest objects in the sky next to the Sun.
Now let's travel to the Martian moons to view Mars. As you already imagine Mars will be huge in the sky due to the proximity of both moons. If you could stand on Phobos you would see Mars 42.5° wide - 85 times the full Earth moon.
Likewise, from Deimos, Mars is still 16.7° in diameter - over 33 times the full Earth moon. From both martian moons, this is a fantastic view. Reflected light from Mars' red surface will provide stunning Mars shine on the night side of both moons. Our moon, too shines onto Earth but by different standards and less spectacular.
Assuming we could stand on Phobos to watch Deimos or on Deimos to gaze at Phobos we would expect a performance of fast changes, because we know that both moons are rapid orbiters. Probably, we would have more fun on Deimos watching Phobos swing around Mars three times a day.
How big we see Phobos from Deimos is a matter of distance which can vary between 14,081km when Phobos is between Mars and Deimos and 32,837km when Phobos is behind Mars. At shortest distance Phobos would appear 6.59 arc minutes wide and 2.83 arc minutes at farest distance. In comparison, Deimos as seen from Phobos would appear 3.66 and 1.57 arc minutes, respectively.
Now the problem with small bodies closely orbiting the comparitively large planet Mars at low inclination is that you can't see either Phobos or Deimos at all times. From the short distance of Phobos, Mars is a big guy to hide behind. In fact, Deimos cannot be seen from Phobos unless its eastern or western elongation from Mars exceeds 20°. Deimos is further out and requires that Phobos elongates over 8° east or west. Basically, these are the angular radii of Mars as seen from each moon.
Taking advantage of extra solar energy collected during the day, NASA's Mars Exploration Rover Spirit settled in for an evening of stargazing with its panoramic cameras, photographing the two moons of Mars as they crossed the night sky.
The two identical cameras are equipped with a 38mm (focal ratio f/20) lens matched to a 1024 by 1024 pixels CCD yielding a 16.8° field of view, consequently a resolution of ca. 59 arc seconds per pixel. This field resembles a conventional 35mm SLR with a 125mm lens.
Spirit's pancam took this image of Orion with a 60 seconds exposure from Columbia Hills, Gusev Crater. The field of view confirms the simulated view above. Orion is "upside down" because the Gusev crater is situated some 15 degrees south of Mars's celestial equator.
Spirit's location projected on Earth is a point 300 km west off Samoa's coast in southern hemisphere. On Mars, Orion lies completely south of the celestial equator, while Earth's equator passes near the star Mintaka in Orion's belt splitting Orion into a northern and a southern part.
The field of view of a camera configuration depends on the size of film or CCD chip and the focal length of the lens. The FOV is mathematically obtained by:φ = Atn(x/fl)
Researchers used the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity to capture this view of comet C/2013 A1 Siding Spring as it passed near Mars on Oct. 19, 2014. This image is from a 50-second exposure taken about two-and-a-half hours before the closest approach of the comet's nucleus to Mars. The sky was still relatively dark, before Martian dawn. At the time of closest approach, the morning sky was too bright for observation of the comet. The comet, some nearby stars, and some effects of cosmic rays hitting the camera's light detector are labeled.
The image has been processed by removal of detector artifacts and slight twilight glow. The duration of the exposure resulted in a 12.5-pixel smear from rotation of Mars. The smear for the comet is at a slightly different angle from the others, due to the comet's own motion across the sky.
A Martian dust storm to the west of Opportunity hampered visibility somewhat on Oct. 19, compared to the sky over Opportunity a week earlier.
Discovered on January 3, 2013, C/2013 A1 (Siding Spring) is an up to 3km wide comet coming from the Oort Cloud along a roughly 1-million-year orbit. On October 19, 2014 at 18:28UT, the comet passed Mars at a speed of 56km/s within 139,500km (84,000 miles), which is about a third of the Moon's distance from Earth and less than one-tenth the distance of any known comet flyby of Earth. The comet will made its closest approach to our Sun on October 25, 2014, at a distance of 130 million miles, well outside Earth's orbit.
With the altazimuth mount fixed on a US$400 million rover, this is a quite formidable observatory running under remote control on another world.
Tracking of the sky for long exposures was not intended per Spirit's job description because the cameras are provided for the purpose of
photographing martian soils. Nevertheless, the results are manifold and remarkable.
Image credit: NASA/JPL/Cornell/Texas A&M
Phobos rising and Deimos setting just above the horizon in the west in the pre-dawn hours of Spirit's Sol 682 (Dec. 3, 2005). Remember that Phobos orbits 3 times faster than Mars rotates, in that Phobos rises in the west and sets in the east. Deimos orbits in less time than a planet rotation, therefore rising and setting 'normally'.
This time-lapse composite, acquired the evening of Spirit's martian sol 585 (Aug. 26, 2005) from a perch atop "Husband Hill" in Gusev Crater, shows Phobos, the brighter moon, on the right, and Deimos, the dimmer moon, on the left. Tiny streaks mark the trails of background stars moving across the sky or the impact of cosmic rays lighting up random groups of pixels in the image.
Spirit took this succession of images at 150-second intervals from a perch atop "Husband Hill" in Gusev Crater on martian day, or sol, 594 (Sept. 4, 2005), as the faster-moving martian moon Phobos was passing Deimos in the night sky. Phobos is the brighter object on the left and Deimos is the dimmer object on the right. The bright star Aldebaran and some other stars in the constellation Taurus are visible as star trails. Most of the other streaks in the image are the result of cosmic rays lighting up random groups of pixels in the camera.
In this image, both martian moons, Deimos on the left and Phobos on the right, travel across the night sky in front of the constellation Sagittarius which in part resembles an upside-down teapot. In this view, Phobos moves toward the handle and Deimos moves toward the lid. Each of the stars in Sagittarius is labeled with its formal name. The inset shows an enlarged, enhanced view of Phobos, shaped rather like a potato with a hole near one end. The hole is the large impact creater Stickney, visible on the moon's upper right limb. Spirit acquired these enhanced-brightness images on the night of sol 585 (Aug. 26, 2005).
In this view the Pleiades, a star cluster also known as the "Seven Sisters," is visible in the lower left corner. The bright star Aldebaran and some of the stars in the constellation Taurus are visible on the right. Spirit acquired this image the evening of martian day, or sol, 590 (Aug. 30, 2005). Within the enhanced halo of light is an insert of an unsaturated view of Phobos taken a few images later in the same sequence.
Scientists will use images of the two moons to better map their orbital positions, learn more about their composition, and monitor the presence of nighttime clouds or haze. Spirit took the five images that make up this composite with the panoramic camera, using the camera's broadband filter, which was designed specifically for acquiring images under low-light conditions.
NASA's Mars Exploration Rover Spirit observed the Martian moon Phobos entering the shadow of Mars during the night of the rover's 675th sol (Nov. 27, 2005). The panoramic camera captured 16 images, spaced 10 seconds apart, covering the period from when Phobos was in full sunlight to when it was entirely in shadow. As with our own Moon during lunar eclipses on Earth, even when in the planet's shadow, Phobos was not entirely dark. The small amount of light still visible from Phobos is a kind of "Mars-shine" -- sunlight reflected through Mars' atmosphere and into the shadowed region.
This view is a time-lapse composite of images taken 20 seconds apart, showing the movement of Phobos from left to right. (At 10 seconds apart, the images of the moon overlap each other.) Scientists are using information about the precise timing of Martian moon eclipses gained from observations such as these to refine calculations about the orbital path of Phobos. The precise position of Phobos will be important to any future spacecraft taking detailed pictures of the moon or landing on its surface.
Image credit: NASA/JPL/Cornell/Texas A&M
On October 25, 2005, Spirit imaged the southern celestial pole of Mars with a composite of nine 60 second untracked exposures. The image shows several trails and marks that could stem from meteors or cosmic rays. While meteor trails often draw a similar direction from a common point of origin, cosmic rays travel from all directions. These high energy particles are generated by the Sun and other stars, annoyingly for amateur images, but of high value for scientific purposes to predict the rate and intensity of cosmic rays striking Mars, knowledge of which gives clues on water ice and dust cloud concentrations during martian nights.
While the constellations over Mars are the same, the positions of the planets are much different from the vantage point of Mars.When observing the solar system planets from Earth we see two inner planets - Mercury and Venus. Mars adds a further inner planet - the Earth - which, as seen from Mars, has the largest elongation (46° at greatest elongation, Mars at perihelion) from the Sun because its orbit is wider than that of Venus and Mercury. As with all inner planets Earth shows phases from 0 to 180 degrees, just like the phases of Venus we observe from Earth.
On Mars, Earth and the Moon would appear as a naked eye double-planet. Since Earth is an inner planet like Venus (a "morning star" or "evening star") observers on Mars can rarely view transits of Earth across the Sun. The next transit is predicted for November 10, 2084, the last transit occurred on May 11, 1984. The image above shows the transit of Venus on June 8, 2004. If Venus were Earth and imaged on Mars, Earth's disk passing in front of the Sun would exhibit nearly the same size with the difference being that the Sun is only 2/3rd wide.
As when we watch planets from Earth we are looking into the past when we observe Earth from Mars. That is because the light from a planet travels over hundreds of millions kilometers, while the speed of light is near 300,000 kilometers per second. Pluto is over 39 AU out there at the edge of the Solar System. The light from Pluto then takes over five hours to reach us. Consequently, we observe Pluto as it was over five hours ago. Now, Earth won't get that far away from Mars, yet it's light takes several minutes. The actual time depends on the distance and can vary roughly between 3 and 22 minutes. The light from the Sun travels 12.7 minutes to Mars at average distance.
Let's assume a 'worst case'. Earth is 22 light minutes away from Mars. You slew your large telescope pinpoint on Earth and find that Tokyo lies straight underneath the central meridian. Behold, what you see is what was 22 minutes ago. Earth rotates once in 24 hours or 360° around from west to east. In other words, 1° in 4 minutes. During an interval of 22 minutes Earth rotates 5.5° towards east. Therefore, whilst you see Tokyo in the center, the real central meridian crosses over Okayama and Shikoku, over 500 km in the west on that latitude (35° north). Of course, the same phenomena is experienced when observing the planets from Earth. Astronomy software usually compensates for the light time presenting the central meridian as if viewed through a telescope -- on Earth.
Depending on each other's orbit positions, the distance between Mars and Earth can vary between 0.36 and 2.68 AUs. Every 2.2 years the two planets near to a close approach. The closest approach since some 60,000 years occured in August 27 in 2003 shrinking the inter-planetary distance to mere 55.758 million km (0.37319AU) at 09:51 UTC (or 3.1 light minutes). While we observed Mars fully illuminated, an observer on Mars would see a dark Earth because the Sun, Earth and Mars are straight aligned, with the Sun shining behind Earth as seen from Mars (orbital inclinations to the ecliptic ignored).
Specifically, at this event, Earth showed Mars its Pacific Ocean at night from its location in the center of the constellation Leo. While Mars was 25.1 arc second wide in Aquarius, the apparent size of Earth from Mars was nearly twice wider, namely 47.13 arc seconds - the scale of a close Jupiter seen from Earth. This is simply due to Earth's diameter, which is about twice of Mars's.
On May 19th, 2005, NASA's Mars Exploration Rover Spirit captured this stunning view as the Sun sank below the rim of Gusev crater on Mars. This Panoramic Camera (Pancam) mosaic was taken around 6:07 in the evening of the rover's 489th martian day, or sol. Spirit was commanded to stay awake briefly after sending that sol's data to the Mars Odyssey orbiter just before sunset. This small panorama of the western sky was obtained using Pancam's 750-nanometer, 530-nanometer and 430-nanometer color filters. This filter combination allows false color images to be generated that are similar to what a human would see, but with the colors slightly exaggerated.
In this image, the bluish glow in the sky above the Sun would be visible to us if we were there, but an artifact of the Pancam's infrared imaging capabilities is that with this filter combination the redness of the sky farther from the sunset is exaggerated compared to the daytime colors of the martian sky. Because Mars is farther from the Sun than the Earth is, the Sun appears only about two-thirds the size that it appears in a sunset seen from the Earth. The terrain in the foreground is the rock outcrop "Jibsheet", a feature that Spirit has been investigating for several weeks (rover tracks are dimly visible leading up to Jibsheet). The floor of Gusev crater is visible in the distance, and the Sun is setting behind the wall of Gusev some 80 km (50 miles) in the distance.Text courtesy NASA/JPL-Caltech
Some 4 billion years ago, when Earth was still completely covered by oceans, the surface of Mars was probably covered by both, oceans and land masses with rivers and primitive sea fauna and flora. A planet covered entirely by water can hardly develop lifeforms. Cohesion of organic matter in water is difficult, because organic matter connects by means of water molecules attached to it and separate upon cohesion. This hardly works in pure water.
Meanwhile, it was easier for Mars, with its oceans and continents to support life long before Earth. Rivers on land flow and dry out repeatingly. In dry environments and in absense of water, organic matter can grow. If that was the case with Mars, life could have been brought from Mars to Earth, for instance by asteroid impacts that whirled up rocks carrying organic matter into space that headed for Earth and felt into its ocean.
Comets are known to carry organic matter and did impact on both Mars and Earth. On Earth, comets felt into the ocean while Mars provided the more favorable environment to bring up life before continents formed on Earth.
The composition of Mars' atmosphere, axial tilt, sun distance, etc., at that time is unknown and will probably remain unknown, in that this chapter is speculative.