User Tools

Site Tools


photo:mars

the planet Mars

introduction

Mars facts

  • sidereal period = 687 days (how long it takes to complete a full revolution around the sun)
  • synodic period = 779.8 days (time taken from one conjunction to another as seen from earth)
  • equatorial diameter = 6,760km (cw. moon =  3,480km, earth = 12,760km, Jupiter = 142,800km)
  • axial rotation = 24.6hrs
  • mass = 0.107 x earth (cw. moon = 0.012, Jupiter = 317.9)
  • 2 moons - Phobos & Deimos

Opposition of Mars:

  • Mars is closest to earth during an opposition. These occur on average once every 780 days and range in proximity from 56m km to 100m km and thus these are regarded as being “favourable” if close or “unfavourable” if distant.
  • The closer it is the bigger its apparent diameter as seen from earth and thus the easier it is to see surface details and the brighter it becomes.
    • its apparent size ranges from ~4“ at its most distant to 20-25” at opposition (Jupiter is usually about 30-45“)
    • brightness as seen from earth = magnitude -1.8 to - 2.9 depending on distance at opposition down to +1.7 at most distant (cw. brightest star Sirius = -1.58; venus -3.3 to -4.5; Jupiter -0.9 to -2.3; Saturn +1.5 to +0.4;
    • August 27th 2003, it came to 55.758m km, the closest for approx. 60,000 yrs. The next time it will be as close is in 288yrs.

History:

  • named after the Roman god of war because of its reddish tinge, and identified in certain aspects with the Greek Ares, and under it, says the Compost of Ptholomeus, “is borne theves and robbers…nyght walkers and quarell pykers, bosters, mockers, and skoffers; and these men of Mars causeth warre, and murther, and batayle. They wyll be gladly smythes or workers of yron..lyers, gret swerers.”
  • among the alchemists, Mars designated iron.
  • Keppler accepts the probable existence of Mars' two moons - presumably based on Earth having 1 and Jupiter having “four”.
  • 1726: satirist Jonathan Swift in his ”Gulliver's Travels“ talks of Mars' “two moons” 
  • 1877 Mars opposition (the finest since 1845): 
    • Asaph Hall using a 26” refractor discovers Mars' two moons (Phobos & Deimos) by manoeuvring his eyepiece to keep mars out of view and thus from blinding his ability to see the close, much dimmer moons. Another method to attempt to see them is by adding an occulting bar in the eyepiece to block the light coming from Mars.
  • Nov 1879 Mars opposition:
    • Schiaparelli using an 8.6“ refractor in Milan discovers:
      • a tiny white spot he called Nix Olympica (“Snow of Olympus”) which he thought was snow on Olympus Mons, but is actually reflected light of the canopy of orographic clouds over its peak which frequently form over the summit after noon as winds carry warm, moisture-laden air over the peaks with resulting freezing of the water to form ice on the leeward (western) side of the summits. This can be seen in good seeing in a 6” reflector esp. if a blue filter is used to improve contrast. These are most likely to be present when the water vapour content of the atmosphere is greatest - northern hemisphere spring/early summer when polar ice melting & early in southern hemisphere spring when ice in Hellas & Argyre basins is subliming. The clouds may coalesce over the Tharsis mountains forming a W cloud that was 1st reported in 1954. The clouds usually disappear during the cold Martian nights.
      • ribbon-thin canali (“channels”)
      • Ascraeus Lacus (“Lake of Ascra”) - the shield volcano we know know as Ascraeus Mons
  • 1892 Mars opposition:
    • William Henry Pickering using a 13“ refractor in the Andes:
      • charted dozens of additional “lakes”, chiefly at the points where Schiaparelli's canali intersected - a few years later suggested that these might be volcanic craters rather than water
      • found that he could distinguish a dark circular spot against a bright background with a 10” telescope if it subtended an apparent angle of 0.20“, exceeding Dawe's limit based on splitting double stars by a factor of 2.3. When Mars disc has an apparent diameter of 20” (eg at opposition), a feature on Mars 68km in diameter will subtend 0.20“, thus the 3 largest summit calderas should just be within the reach of a 10” telescope in good seeing.
  • 1894 Mars opposition:
    • Edward Emerson Barnard using a 36“ refractor at Lick Observatory atop California's Mount Hamilton:
      • detailed sketches of Martian surface including Arsia Mons, Olympus Mons as dark spots
  • 1898, H.G.Wells wrote The War Of The Worlds, in which he recounted the horrors of a war from invading martians on earth.
  • 1903: Lowell using a 24” refractor when Mars disc was 12.6“ diameter:
    • “global network of irrigation canals” based on his preconceived notion that Mars surface was smooth & level. This optical illusion perpetuated this misconception for many years.
  • most astronomers before space probes obtained close-up images believed it was a windswept wasteland devoid of any dramatic topographic features
  • 1st three Mariner spacecraft that flew past Mars snapped high-resolution images of less than 1/5th of its surface, but unfortunately, this fraction was not a representative sample as they showed bleak, monotonous landscapes peppered with hundreds of eroded impact craters which seemed to verify the dour expectations of a geologically uninteresting world
  • Nov 1971: Mariner 9 space probe orbited Mars to map it from pole to pole, but a global dust storm was raging that gave it the appearance of a featureless ball of orange wool. As the storm abated, a very different world was revealed - summits of 4 enormous volcanoes, looking like islands in a sea of dust. The largest, Olympus Mons, towers to a height of 21.3km - nearly 2.5x height of Mt Everest, with a base of 550km diameter. Its three smaller neighbours, the Tharsis Montes - Ascraeus Mons, Pavonis Mons & Arsia Mons - each rise ~15km and are arrayed in a line known as the Tharsis Ridge.
  • 1976, Viking 1 takes the famous “face on Mars” photo - a rock formation 2.5km wide which gives the illusion of it being a human face, but some developed theories of the Egyptian pyramids especially as the Mariner 9 image showing “pyramids” on Mars in the plain of Elysium which had sides 13x the size of Giza's Great Pyramid in Egypt .
  • 4 of the 6 closest oppositions in the 20thC featured planet-encircling dust storms that shrouded the planet surface for weeks.
  • 1998: Mars Global Surveyor supplied new & revealing images.
  • August 27th 2003, it came to 55.758m km, the closest for approx. 60,000 yrs. The next time it will be as close is in 288yrs.

What can one see on Mars?

  • here is a pic of mars taken from the Hubble Space Telescope without Earth's interfering atmosphere
    • www.ayton.id.au_gary_science_astronomy_mars.jpg
  • below are simulations of how Mars would appear at opposition through telescopes with apertures from 2.4” to 12“ under very good seeing condition and moderate turbulence (more typical of observing conditions):

If you are having difficulties seeing anything but a blob then consider:

1. Are the optics of your scope good quality. Bad optics will never focus sharply and image contrast will always be poor. In a reflecting telescope if the mirror is homemade, has it been tested so that you know if it can perform well?

2. Collimation, (optical alignment) could be the problem. Visit this site on how to fix this and many other telescope problems. http://astronomy.trilobytes.com.au/scope/fix-it.htm

3. Bad seeing (turbulence). If Mars is low in the sky, atmospheric turbulence can obliterate contrast and detail on the planet. Wait for it to gain altitude say greater than 30 degrees. Sometimes seeing may be bad even when Mars is high. It depends on atmospheric conditions at the time.

4. Speaking of turbulence. Thermal currents inside the telescope tube will have a similar effect if the scope is transported from a warm interior to cold outdoors. Allow the scope 1/2hr to 1hr to reach thermal equilibrium outdoors before beginning to search for planetary detail.

5. Even in an 8” with good optics and good seeing conditions the dusky markings on the planet require some patience and practice to discern especially if you are new to observing. The bright polar cap however should be easily visible.

6. In a 3.5“ Maksutov, The polar cap is always visible and the most prominent markings (Sinus Sabius, Syrtis  Major, Mare Sirenum, Mare Cimmerium and the dark hood around the ever  shrinking polar cap) are identifiable most of the time. They are better with a homemade 6” Newtonian.

7. Sometimes a larger aperture performs worse than a smaller aperture under bad seeing conditions. You may have been caught out by this. It depends on the prevailing general seeing conditions in your locality which may be determined by season, adjacent buildings, bodies of water, vegetation and other such factors. You might like to try a 4“ or 6” aperture mask over the top end of the scope to see if this beats the seeing conditions. It might also cure a badly figured homemade mirror if that is the problem.

8. A red or orange filter will help if the seeing is good to begin with. Otherwise it makes little difference. On a recent occasion an orange filter improved the contrast on Mars in the 3.5“ Maksutov but made no difference in the 6”. A filter however, even if it does nothing else, can reduce the “glariness” of the planet so that it is easier on the eye. 

9. Provided the optics in your scope are good to begin with, keep on persisting with the above points in mind and you are sure to get a good night when Mars will deliver! As a rule, with good optics, under good seeing conditions, a larger aperture will always outperform a smaller one.

Martian ice ages:

  • NASA's Mars Global Surveyor and Mars Odyssey missions have provided evidence of a recent ice age on Mars. In contrast to Earth's ice ages, a martian ice age waxes when the poles warm up and water vapor is transported toward lower latitudes. Martian ice ages wane when the poles cool and lock water into polar icecaps.
  • The “pacemakers” of ice ages on Mars appear to be much more extreme than the comparable drivers of climate change on Earth. Variations in the planet's orbit and tilt produce remarkable changes in the distribution of water ice from polar regions down to latitudes equivalent to Houston or Egypt.
  • Researchers, using NASA spacecraft data and analogies to Earth's Antarctic Dry Valleys, report their findings in the Thursday, Dec. 18 2003 edition of the journal Nature. “Of all the solar system planets, Mars has the climate most like that of Earth. Both are sensitive to small changes in orbital parameters,” said planetary scientist Dr. James Head of Brown University, Providence, R.I., lead author of the study. “Now we're seeing that Mars, like Earth, is in a period between ice ages.”
  • Discoveries on Mars, since 1999, of relatively recent water- carved gullies, glacier-like flows, regional buried ice and possible snow packs created excitement among scientists who study Earth and other planets. Information from the Mars Global Surveyor and Odyssey missions provided more evidence of an icy recent past.
  • Head and his co-authors from Brown (Drs. John Mustard and Ralph Milliken), Boston University (Dr. David Marchant) and Kharkov National University, Ukraine (Dr. Mikhail Kreslavsky) examined global patterns of landscape shapes and near-surface water ice mapped by the orbiters. They concluded that a covering of water ice mixed with dust mantled the surface of Mars to latitudes as low as 30 degrees, and is now degrading and retreating. By observing the small number of impact craters in those features and by backtracking the known patterns of changes in Mars' orbit and tilt, they estimated the most recent ice age occurred just 400,000 to 2.1 million years ago, very recent in geological terms. “These results show that Mars is not a dead planet, but it undergoes climate changes that are even more pronounced than on Earth,” Head said.
  • Marchant, a glacial geologist who has spent 17 field seasons in the Mars-like Antarctic Dry Valleys, said, “These extreme changes on Mars provide perspective for interpreting what we see on Earth. Landforms on Mars that appear to be related to climate changes help us calibrate and understand similar landforms on Earth. Furthermore, the range of microenvironments in the Antarctic Dry Valleys helps us read the Mars record.”
  • Mustard said, “The extreme climate changes on Mars are providing us with predictions we can test with upcoming Mars missions, such as Europe's Mars Express and NASA's Mars Exploration Rovers. Among the climate changes that occurred during these extremes is warming of the poles and partial melting of water at high altitudes. This clearly broadens the environments in which life might occur on Mars.”
  • According to the researchers, during a martian ice age, polar warming drives water vapor from polar ice into the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. This ice-rich mantle, a few meters or yards thick, smoothes the contours of the land. It locally develops a bumpy texture at human scales, resembling the surface of a basketball and also seen in some Antarctic icy terrains. When ice at the top of the mantling layer sublimes back into the atmosphere, it leaves behind dust, which forms an insulating layer over remaining ice. On Earth, by contrast, ice ages are periods of polar cooling. The buildup of ice sheets draws water from liquid-water oceans, which Mars lacks. “This exciting new research really shows the mettle of NASA's 'follow-the-water' strategy for studying Mars,” said Dr. Jim Garvin, NASA's lead scientist for Mars exploration. “We hope to continue pursuing this strategy in January, if the Mars Exploration Rovers land successfully. Later, the 2005 Mars Reconnaissance Orbiter and 2007 Phoenix near-polar lander will be able to directly follow up on these astounding findings by Professor Head and his team.” Global Surveyor has been orbiting Mars since 1997, Odyssey since 2001. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages both missions for the NASA Office of Space Science, Washington, D.C.
  • Information about NASA's Mars missions is available on the Internet at: http://mars.jpl.nasa.gov.
photo/mars.txt · Last modified: 2013/02/01 13:05 by gary1