* Astronomy

Members Login
    Remember Me  
Post Info
TOPIC: Mars Express


Posts: 131433
South Polar Water

New radar observations by MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), aboard the Europe's Mars Express spacecraft, has discovered a large and previously unknown reservoir of water ice extending as deep as 3.5 kilometres below the southern polar cap of Mars.
Previously, water ice was found 1.8 kilometres below the surface of the northern polar ice cap.
In 2004, the OMEGA instrument had discovered steep slopes (scarps) made almost entirely of water ice at the south pole.

Expand (236kb, 1731 x 1380)
A partial (visible) view of the Martian south polar ice cap, taken on 11 February 2004 during orbit 103 by the High Resolution Stereo Camera on Mars Express, from an altitude of 269 kilometres light.
Credits: ESA/DLR/FU

The radar antenna was deployed in June 2005.
Estimates suggest that the polar caps hold enough water to cover the entire planet in a layer of water up to 33 metres deep. It is thought that the water ice layers were deposited as recently as 50,000 years ago during the last glacial period on Mars.

MARSIS also found possible thin layers of underground water ice in regions around the south pole, somewhere where the Martian surface that shows no visible signs of ice.
These suspected regions may contain half of the water ice contained in the southern polar cap. However, it is possible that they actually are just layers of dust.

"If we can confirm the thinner layers are, in fact, ice rich, we've put our finger on another reservoir of water that is significant in the global water matrix" - Jeff Plaut, NASA's Jet Propulsion Laboratory in Pasadena, California, US, MARSIS co-leader.

The new data was presented at the Lunar and Planetary Science Conference (LPSC) in Houston, Texas, on Monday.



Posts: 131433
RE: Mars Express

Mars Express, the spacecraft launched by the European Space Agency into a near Martian orbit, will have been in orbit for two years in January 2006. The mission - the successor to Russia's Mars-96 - has been a major achievement of European and Russian planetary science.
The orbiter successfully entered Martian orbit on 25 December. First it manoeuvred into a highly elliptical capture orbit from which it moved into its operational near polar orbit later in January 2004.
Six days before arrival on 25 December 2003, Mars Express ejected the ill fated Beagle 2 lander which was to have made its own way to its landing site on the surface.



Posts: 131433
Chryse Planitia

With measurements taken only for a few weeks during night-time observations last summer, MARSIS - the Mars Advanced Radar for Subsurface and Ionospheric Sounding - is already adding to our knowledge of the Martian interior.

Expand (165kb, 788 x 683)
Topographic map of Chryse Planitia with location of possible buried basin
The parabolic arcs correspond to ring structures that could be interpreted as the rims of one or more buried impact basins. Other echoes show what may be rim-wall 'slump blocks' or 'peak-ring' features.
Credits: ASI/NASA/ESA/Univ. of Rome/JPL/MOLA

"The detection of a large buried impact basin suggests that MARSIS data can be used to unveil a population of hidden impact craters in the northern lowlands and elsewhere on the planet. This may force us to reconsider our chronology of the formation and evolution of the surface" - Jeffrey Plaut, Co-Principal Investigator on MARSIS.

The topographic map, based on Mars Orbiter Laser Altimeter data, shows the MARS Express ground tracks and the arc structures detected by MARSIS that are interpreted to be part of a buried impact basin about 250 km in diameter. The topographic relief represented in the image is 1 km, from low (purple) to high (red). The projected arcs are shown in red for orbit 1892 and white for orbit 1903. There is no obvious feature in the surface topography that corresponds to the buried feature identified with MARSIS data.

The planar reflection (see previous post) is consistent with a flat interface that separates the floor of the basin, situated at a depth of about 1.5 to 2.5 km, from a layer of overlying different material.
In their analysis of this reflection, scientists do not exclude the intriguing possibility of a low-density, water-ice-rich material at least partially filling the basin.



Posts: 131433
MARSIS radar antenna

The MARSIS radar antenna aboard Europe's Mars Express spacecraft has probed two kilometres below the Martian surface and found tantalising hints of liquid water pooling in a buried impact crater.
The MARSIS antenna was deployed successfully in June 2005.

"This is very experimental. We wondered - can we see anything in the subsurface? The answer to that is yes" - William T K Johnson, MARSIS manager at NASA's Jet Propulsion Laboratory in Pasadena, California, US.

The MARSIS antenna revealed subsurface features at two regions in the planet's northern hemisphere – the mid-latitude lowlands called Chryse Planitia and the northern polar cap.
A 250-kilometre-wide circular structure that lies between 1.5 and 2.5 kilometres below the surface of Chryse Planitia is perhaps an impact crater that was buried with volcanic ash or soil several billion years ago.

This MARSIS image reveals a 250-km-wide buried impact basin.

No radar boundaries in material that fills the bowl of the crater are seen, and the radar signals lose little strength when passing through it. That suggests the infill must contain a large proportion of ice, which is nearly transparent to radar.
Substantial amounts of ice in the soil would make sense given the crater's location in what appears to be a basin where ancient rivers once converged.

"If the water could be captured in a basin and preserved for several billion years, it may still be there" - Jeff Plaut, NASA's Jet Propulsion Laboratory in Pasadena, California, US.

Intriguingly, the signal reflected from the bottom of the crater is so strong and appears so flat that it may be liquid water.

In this image, a linear reflection nearly parallel to the surface is seen embedded in the arcs – this may be the result of liquid water.
Image: ASI/NASA/ESA/Univ of Rome/JPL.

"If you put water there, that's what the signal might look like" - William T K Johnson.

However, the data is based on only one pass over the region and could be caused by another material.
MARSIS also studied the northern polar cap and found nearly pure water ice stretching down 1.8 kilometres below the surface, with an icy layer of sand underneath.
The researchers are encouraged that such interesting features have emerged from only three data-gathering passes. MARSIS has only been able to make this small number of observations because the subsurface results can only be obtained under special circumstances.
MARSIS can operate best when it is closest to Mars - which is just 26 minutes of each 7-hour orbit – and when it is also on the planet's "night" side. This is because energetic electrons in the sunlit portions of the planet's outer atmosphere, or ionosphere, block the radar's longest, ground-penetrating wavelengths.

1.8 km thick icy deposits at the north pole. The deposits appear as a layer on the right of the upper image
Credit: ASI/NASA/ESA/Univ. of Rome/JPL/MOLA Science Team

For the last several months, these conditions have not existed at all. But, the conditions are now right again and will remain so until May 2006. The next study regions are in the southern hemisphere, including the south pole.

But gathering the data is only the first step – it then has to be interpreted, which can take scientists months. That is because radar signals travel at different speeds through the ionosphere depending on their wavelength, and the ionosphere itself varies in size depending on the Sun's activity.

"The ionosphere is always around pestering us" - William T K Johnson.

So far the ionosphere has prevented the instrument's longest wavelengths – which could reach down as far as five kilometres - from returning data.

-- Edited by Blobrana at 19:28, 2005-11-30



Posts: 131433
RE: PFS broken

One of the best chances for solving Mars's methane mystery may have been lost. The Planetary Fourier Spectrometer (PFS) on board the Mars Express orbiter seems to be broken, perhaps for good.

The instrument's failure would be a blow for scientists who want to find out how the red planet is producing the methane that has been detected in recent years.

Almost all the methane on Earth comes from some sort of biological source. As a methane molecule typically survives for only a few hundred years in the Martian atmosphere, something must have been spewing it out recently, scientists reason. And this has fuelled hopes for discovering life on Mars.

But scientists have recorded very different methane levels with different techniques. In 2004, the PFS found that methane averaged abut 10 parts per billion in Mars's atmosphere, suggesting that more than 100 tonnes of the gas is released from the surface each year. That same year, Mike Mumma of NASA's Goddard Space Flight Centre in Maryland spotted levels of 250 parts per billion using a telescope in Hawaii. This week he told an American Astronomical Society meeting in Cambridge that he had spotted levels of 44-63 parts per billion from a different part of the planet.

To pin down the source of the gas, these disagreements need to be sorted out. One explanation might be that methane is venting intermittently from specific points on the surface. To check, researchers hope to take simultaneous readings of exactly the same place using both orbiting and earth-based instruments.

But the chance to do this may now be lost, says Thérèse Encrenaz, of the Paris Observatory in France, who is part of the PFS team. She says that the spectrometer has been in trouble for two months, and various attempts to fix it have proven fruitless.

"There's still a chance it could be fixed. But if it cannot be fixed then the experiment will be stopped" - Thérèse Encrenaz.

Ludmilla Zasova of the Space Research Institute in Moscow, says the instrument stopped working some time in July. "It's a problem with the vibration of the spacecraft," says Zasova, who leads the Russian contingent of scientists working with the PFS. These vibrations have shown up in PFS data for the duration of the mission, although scientists have been able to filter out the effects to generate clean results. Zasova thinks the vibrations are affecting a pendulum inside the instrument that helps to control the way it collects light.

But team members are unclear about the severity of the problem. Vittorio Formisano of the Institute of Physics and Interplanetary Science in Rome, Italy, would not confirm that it is broken. Formisano is in charge of the instrument and says he is being kept busy working on it.

This isn't the first trouble that Mars Express has had. The European Space Agency's craft had difficulty opening some radar booms needed for its water detection experiment in May, although these are now working well.

And there have been controversies surrounding interpretation of data from the spectrometer. In February of this year, Formisano said that the PFS had found large quantities of formaldehyde around Mars. This implied that millions of tonnes of methane were being released by the planet each year: much, much more than thought. Encrenaz says most scientists now agree that these claims about formaldehyde were incorrect.

Without nailing the methane numbers, it will be hard for all scientists to agree on a source for the gas. For now, many say it is probably due to heating of water and carbon dioxide with a mineral called olivine, rather than life, says Sushil Atreya, a member of the PFS team from the University of Michigan in Ann Arbor.

If the Mars Express methane instrument fails to provide further data, the next opportunity will be NASA's Mars Science Laboratory, due to blast off in 2009. This will not only measure trace levels of methane, but also check its isotopic make-up for signs of biological activity.




Posts: 131433
RE: Marsis

Marsis, the sounding radar onboard ESA's Mars Express spacecraft, is collecting the first data about the surface and ionosphere of Mars.

This radar started its science operations on 4 July, the same day as its first commissioning phase ended. Due to the late deployment of Marsis, it was decided to split the commissioning, originally planned to last four weeks, into two phases; the second will take place in December. It has thus been possible to begin scientific observations with the instrument earlier than initially planned, while it is still Martian night-time. This is the best environmental condition for subsurface sounding, as in daytime the ionosphere is more 'energised' and disturbs the radio signals used for subsurface observations.

As from the start of commissioning, the two 20m-long antenna booms have been sending radio signals towards the Martian surface and receiving echoes back.
"The commissioning procedure confirmed that the radar is working very well and that it can be operated at full power without interfering with any of the spacecraft systems" - Roberto Seu, Instrument Manager for Marsis, of University of Rome 'La Sapienza', Italy.

Marsis is a very complex instrument, capable of operating at different frequency bands. Lower frequencies are best suited to probing the subsurface, the highest frequencies are used to probe shallow subsurface depths, while all frequencies are suited to studying the surface and the upper atmospheric layer of Mars.

"During commissioning we worked to test all transmission modes and optimise the radar's performance around Mars. The result is that since we started the scientific observations in early July, we have been receiving very clean surface echoes back, and first indications about the ionosphere" - Professor Giovanni Picardi, Principal Investigator for Marsis, of University of Rome 'LaSapienza'.

The Marsis radar is designed to operate around the orbit 'pericentre', when the spacecraft is closer to the planet's surface. In each orbit, the radar is switched on for 36minutes around this point, spending the middle 26minutes on subsurface observations and the first and last five minutes of the slot on active ionosphere sounding.
Using the lower frequencies, Marsis has been mainly investigating the northern flat areas between the 30° and 70° latitudes, at all longitudes.

"We are very satisfied with the way the radar is performing. In fact, the surface measurements taken so far match almost perfectly the existing models of the Mars topography. As the radar appears to work so well for the surface, we have good reason to think the radio waves are also propagating correctly below the surface. The bulk of our work has just started, as we now have to be sure to clearly identify and isolate the echoes coming from the subsurface. To do this, we have to carefully screen all data and make sure that signals which could be interpreted as coming from different underground layers are not actually produced by surface irregularities. This will keep us occupied for a few more weeks at least " - Professor Giovanni Picardi.

Thus, these measurements have proved to be an excellent test. The scientific reason for concentrating on flat regions with the first data analysis is the fact that the subsurface layers are in principle easier to identify, though the task is still a tricky one.
The first ionospheric measurements performed by Marsis have also led to some interesting preliminary findings. The radar responds directly to the number of charged particles composing the ionosphere (plasma). This has at times been shown to be higher than expected.

We are now analysing the data to find out if such measurements may result from sudden increases in solar activity, such as the one observed on 14July, or if we have to put forward new hypotheses. Only further analysis of the data can tell us" - Jeffrey Plaut, co-Principal Investigator, from the NASA Jet Propulsion Laboratory, Pasadena, USA.

Marsis will carry on sending signals that hit the surface and penetrate the subsurface until the middle of August, when the night-time portion of the observations will have almost ended. After that, observation priority will be given to other Mars Express instruments that are best suited to operating in daytime, such as the HRSC camera and Omega mapping spectrometer. However, Marsis will continue its surface and ionospheric investigations in daytime, with ionospheric sounding being reserved for more than 20% of all Mars Express orbits, under all possible Sun illumination conditions.
In December, the Mars Express orbit pericentre will enter night-time again. By then, the pericentre will have moved closer to the south pole, allowing Marsis to carry out optimal probing of the subsurface once again, this time in the southern hemisphere.
The first commissioning phase was given over to testing the Marsis electronics and software and the two 20m-long antennas (dipole).
The second commissioning phase, lasting about ten days, will be spent calibrating the 7m 'monopole' antenna. This antenna is to be used in conjunction with the Marsis dipole to correct any surface roughness effects caused by the radio waves emitted by the dipole and reflected by an irregular surface. The monopole will find its best use during investigations of areas where surface roughness is greater.

The Marsis instrument was developed within the framework of a Memorandum of Understanding between the Italian Space Agency (ASI) and NASA. It was developed by Alenia Spazio under ASI management and the scientific supervision of University of Rome 'La Sapienza', in partnership with the Jet Propulsion Laboratory (JPL) and the University of Iowa. JPL provided the antenna manufactured by Astro Aerospace. It is the first instrument designed to actually look below the surface of Mars.
Its major goals are to characterise the subsurface layers of sediments and possibly detect underground water or ice, conduct large-scale altimetry mapping and provide data on the planet's ionosphere.
For subsurface probing, Marsis must operate between 300 km and 800 km from the Martian surface, while for ionospheric sounding, it has already provided satisfactory results from a distance of up to 3000 km. Radar vertical resolution is about 150m (in free space), while horizontal resolution, in the range of a few kilometres, depends on the spacecraft's altitude.

The joint Italian and American Marsis team is also largely involved in the Sharad radar, a facility instrument provided by ASI for NASA's Mars Reconnaissance Orbiter (MRO), due for launch in August. Marsis and Sharad are two radars designed to provide complementary information about the Martian subsurface. Marsis can penetrate to an average depth of 5km, while Sharad will concentrate on layers closer to the surface.




Posts: 131433

MARSIS, has undergone its first check-out and is ready to start operations around the Red Planet.

With this radar, the Mars Express orbiter at last has its full complement of instruments available to probe the planet`s atmosphere, surface and subsurface structure.
MARSIS`s ability to transmit radio waves in space was tried out for the first time on 19 June, when the instrument was switched on and performed a successful transmission test.

Before starting its scientific observations, MARSIS has to undergo its commissioning phase. This is a routine procedure for any spacecraft instrument, necessary to test its performance in orbit using real targets in situ.
In this case, the commissioning will last about ten days, or 38 spacecraft orbital passes, starting on 23 June and ending on 4 July.

During the commissioning phase, MARSIS will be pointed straight down (nadir pointing mode) to look at Mars from those parts of the elliptical orbit where the spacecraft is closest to the surface (around the pericentre).
During this phase, it will cover the areas of Mars between 15 degrees S and 70 degrees N latitude. This includes interesting features such as the northern plains and the Tharsis region, so there is a small chance of exciting discoveries being made early on.

On 4 July, when the commissioning operations end, MARSIS will start its nominal science observations. In the initial phase, it will operate in survey mode. It will make observations of the Martian globe`s night-side.
This is favourable to deep subsurface sounding, because during the night the ionosphere of Mars does not interfere with the lower-frequency signals needed by the instrument to penetrate the planet's surface, down to a depth of 5 kilometres.
Through to mid-July, the radar will look at all Martian longitudes between 30 degrees S and 60 degrees N latitude, in nadir pointing mode. This area, which includes the smooth northern plains, may have once contained large amounts of water.

The MARSIS operation altitudes are up to 800 kilometres for subsurface sounding and up to 1200 kilometres for studying the ionosphere.
From mid-July, the orbit's closest approach point will enter the day-side of Mars and stay there until December. In this phase, using higher frequency radio waves, the instrument will continue shallow probing of the subsurface and start atmospheric sounding.

"Overcoming all the technical challenges to operate an instrument like MARSIS, which had never flown in space before this mission, has been made possible thanks to magnificent cooperation between experts on both sides of the Atlantic. The effort is indeed worthwhile as, with MARSIS now at work, whatever we find, we are moving into new territory; ESA`s Mars Express is now well and truly one of the most important scientific missions to Mars to date" - Professor David Southwood, ESA's Science Programme Director.


-- Edited by Blobrana at 14:49, 2005-06-22


RE: Mars Express

The second 20-metre antenna boom of the MARSIS instrument on board Mars Express was successfully - and smoothly - deployed, confirmed today by the ground team at ESA's European Space Operations Centre.
The complete success of the operation was announced today at 14:00 CEST, when the ground team had completed all tests on the spacecraft systems.
This confirmed that the spacecraft is in optimal shape and under control, with the second MARSIS boom straight and locked into the correct position.


(fixed your link - Ed)

-- Edited by Blobrana at 21:40, 2005-06-16



Posts: 131433

In deploying boom 2, mission managers set Mars Express rotating very slowly with the stored boom facing generally towards the Sun.
Then, they deployed the boom and kept rotating the spacecraft so that, in half an hour, the boom rotated through 180 degrees.

"So if you assume a hinge is at an angle somewhere, the Sun would illuminate all the hinges and heat them up" - Fred Jansen, spacecraft's mission manager.

Managers will study data from the spacecraft's gyroscopes, which measure its rotation, to see whether the boom deployed straight. They hope to finish their analysis of the deployment on Thursday.
If the procedure was a success, mission officials will deploy the third and final boom on 17 June.
This is a 7-metre-long pole that will help determine whether the reflected radio waves are coming from underground, but it is not critical to the mission.
If all goes to plan, the experiment is set to record its first data on 21 June, as part of its initial commissioning phase.

MARSIS was originally scheduled to be deployed in April 2004 but was delayed for a year over concerns that the springy booms could have hit and damage the spacecraft during deployment. But further Earth-based tests allayed those fears.


RE: Marsis experiment

The second of three radar booms has been deployed on Europe's Mars Express spacecraft.
If the deployment went smoothly - it is unclear whether the operation has been successful - the Marsis experiment could begin its search for water on 21 June
The antennas are part of the Marsis instrument, which will look beneath the Red Planet's surface for what are expected to be vast reserves of water.
On Tuesday, mission controllers at the European Space Agency's operations centre in Darmstadt, Germany, released the second of two identical, 20m-long booms which comprise Marsis' primary antenna.
They performed a series of manoeuvres designed to heat the boom evenly in sunlight before reorienting the spacecraft towards Earth so it could begin transmitting data.
Controllers should know whether the operation was a success by tomorrow.

«First  <  1 2 3 4 5 6  >  Last»  | Page of 6  sorted by
Quick Reply

Please log in to post quick replies.

Create your own FREE Forum
Report Abuse
Powered by ActiveBoard