Hellas Planitia

Published on Feb 4, 2008 at 3:35 pm. 7 Comments.
Filed under Mars, planets.

A few days ago, I wrote about Mercury’s Caloris Basin. It is mind boggling huge. Naturally, as Darnell Clayton of Colony Worlds asked, it is natural to wonder if this is the largest impact basin in the Solar System. As it turns out, there are larger impact structures. The largest may by our own Moon’s South Pole-Aitken Basin. I will write about that next. Instead, I wanted to focus this posting on Mars’ Hellas Planitia (or Hellas Basin).
Mars

Measuring nearly 2300 kilometers across, the Hellas Basin is one of the largest impact features in the Solar System. The floor of the basin is almost 7 kilometers below what would likely have been the original terrain level, and its rims extend upward for 2 kilometers. That means that it is 9 kilometers (almost 6 miles) from the floor of the basin to its rim!

Hellas Planitia is so deep that the atmospheric pressure at its bottom reaches nearly 1160 Pascals. That is comfortably above the triple point of water, meaning that if the temperature were high enough, then liquid water could exist at the floor of the basin. However, at Hellas Planitia’s southern latitude, the temperature is believed to seldom, if ever, get that warm. Still, it suggests that perhaps that is a good place to look for any liquid water, if any might be left on Mars.

Hellas Planitia is to large that it can be seen from Earth as a bright oval region in the southern hemisphere of Mars. The name “Hellas” makes reference to Greece, and the name was bestowed onto the bright region by the famous astronomer Giovanni Schiaparelli.

Hellas Basin

The floor of the basin shows few craters. This really stands out compared with the heavily cratered highlands of the southern hemisphere. There are also apparently volcanic flow features on the floor of the basin similar to some of the “wrinkles” and ridges seen on the lunar seas. This suggests significant volcanic modification of the basin floor. It would be very interesting to see if the rocks in the floor of the crater were dark colored basalts like those of the lunar seas, or more light colored rocks that seem to form Caloris Basin on Mercury. At any rate, it would be very tough to tell from orbiting spacecraft. Mars does have an atmosphere, and the ubiquitous dust of Mars no doubt has covered the surface layers of the rock with a significant layer of dust. That gives it the lighter colored appearance.

Such a large impact, though, has far reaching consequences. Massive amounts of ejecta from the impact stretches across Mars to a distance of at least 4000 kilometers from the basin’s center. In places, the ejecta may be up to 2 kilometers thick. If all of that ejecta were piled up on Earth, it would cover the entire North American continent to a depth of well over 1 kilometer. No doubt, some of the ejecta from such an impact actually rained down across the entire Martian surface.

It is interesting to note that the Hellas impact basin is on the other side of Mars from the Tharsis region of Mars, with its monstrous volcanoes (including Olympus Mons, the largest volcano in the Solar System). Several people have suggested a link between the two, but that appears unlikely. For one thing, Hellas Planitia is not exactly opposite the Tharsis rise. Also, the volcanoes of Tharsis are likely hot spot volcanoes, not something triggered by seismic activity. So, it is likely just coincidence that the two features are on separate sides of Mars. However, Tharsis and Hellas both contribute heavily to the features on Mars, and both are likely major factors in the evolution of the climate and topology of the planet.

-Astroprof

Images courtesy NASA, JPL, STScI

7 Comments to ‘Hellas Planitia’:

  1. Rick Laviolette on May 30, 2008 at 6:32 pm: 1

    The Hellas Basin and its opposite side of Tharsis Montes give me the impression that the “bullet” hit and caused: 1. 4 Km drop in surface height 2. The Tharsis Montes Bulge on the opposite side of the Planet 3. The Tectonic crack called Valles Marinaris and the gigantic Olympus Mons Volcano as well as 2 others. So my impression is of a planet that took a bullet and died. All of its water either streamed into space or froze into the ground. Great article.

  2. Mark C on May 11, 2009 at 11:26 am: 2

    I may have a partial smoking gun, after skiming A.J. Connell’s core shift data pdf and a Donald Wise paper Quote: “(2) evolution of the Tharsis bulge. Tharsis development apparently involved two stages: (1) an initial rapid topographic rise accompanied by the development of a vast radial fault system, and (2) an extremely long-lived volcanic stage”

    And My ‘What if’ connection: Shumacher-levy fragment type event impactor / near miss by white dwarf fragments: Proposed: White Dwarf Impactor at Hellas Planitia 40 deg S expended sub Tharsis region 12 deg S leading core shift (Connell) and drawn toward near miss dwarfs concurrently forming Valles Marineris. A casting of Hellas volume compared to Tharsis projection might prove a close match. As to trajectory not matching? I see how orbit, rotation and gravitic shear curves trajectory toward end of near miss path (V. Marinaris W 6 miles deep) fits a shot of .3b years past; Some of the 7 Dwarfs may have changed Earth’s gravitional constant and ‘grounded’ suddenly overweight dinosaurs.

    Lots of intriguing permutation to this model - probably grant funds as well, could use that myself.

    Mark

  3. Mark C on May 11, 2009 at 11:35 am: 3

    Well, that ate 1/2 a paragraph:

    “curves trajectory toward end of near miss path (V. Marinaris W 6 miles deep) fits a shot of…” less than 5 cubic mile white dwarf bullet at a weight of .1 trillion short tons impactor pulling the dirt in after it creating the Hellas Planitia Subduction.

    If the lack of old impacts in Hellas are less than…” .3b years past; Some of the 7 Dwarfs may have changed Earth’s gravitional constant and ‘grounded’ suddenly overweight dinosaurs.

    I must have used less than and greater than symbols inadvertantly self editing my post (

  4. Jonny on July 15, 2009 at 7:30 am: 4

    “I am really really really getting tired of being stuck in this cradle. I want to go outside, explore and play.” (spoken on behalf of the human race with respect to Earth)

    I was really excited to observe a possible connection between Tharsis and Hellas. Seems to me the only plausible explanation for a pair of the solar system’s most exaggerated features.

    I’m building a strategy video game around all this stuff, so now and then I dig a little deeper for interest-sake and wonder.

  5. The Mars life exploration – Hellas Planitia « Newsicare on June 8, 2010 at 10:31 am: 5

    […] also can find this article is useful for discussing the technical details of Hellas […]

  6. bo0b on January 10, 2011 at 4:11 pm: 6

    4567455555555555555554444452428234684435438958953893333

  7. mike l on September 28, 2011 at 3:25 am: 7

    You have an interesting article. I appreciate how informative it is. I have recently read that the Mars Reconnaissance Orbiter has discovered what is thought to be water ice glaciers on the south east side of the basin, which if so make hellas the ideal spot for human habitation on Mars. I am wondering how far hellas is from the south pole. I have not been able to find that data. If you know or can direct me to someone who does I would appreciate it as most maps measure elevation and seem to ignore distance.

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