Earth seen from Mars: We are here

As you have seen from our recent blog posts and Flickr updates, VMC has been busy capturing some spectacular views of Mars.

However on 3 July, we once again turned away from Mars to look towards a more distant target.

Earth seen from Mars. Credit: ESA/Mars Express/VMC

Earth seen from Mars. Credit: ESA/Mars Express/VMC

Ever since our successful test of the VMC camera's long exposure mode (which brought us our first direct images of Phobos), there's one observation we've been keen to attempt:

An image of Earth!

Our chance observation of Jupiter in April served double duty as a dry run to evaluate if VMC stood a chance of detecting the famous pale blue dot.

With the success of the Jupiter pictures, we felt there was a good possibility that, whilst Earth would likely be faint, it would just be visible.

However, imaging Earth from a Mars-orbiting spacecraft using a camera with no specialised optics is not as simple as it sounds. So we thought we'd provide a brief overview of the kind of things that go into taking a picture like this.

One of the first issues we had deal with was determining the optimal time to take the photo.

Earth and Mars are both orbiting the Sun at different rates, so the angle between them regularly gets larger then smaller.

The larger the Mars-Sun-Earth angle, then – when viewed from Mars – the larger the percentage of Earth that is illuminated. So, you might conclude that we should take the image when this angle as big as possible.

However there are two problems with this:

  1. If this angle is very large, then Earth is much further away from Mars and thus will appear much smaller.
  2. The larger this angle gets, when we look towards Earth from Mars, the narrower the Mars/Sun angle gets. This means that the Sun will then be in the field of view of the camera.

This is not only prohibited in the interests the safety of our instruments but would also mean imaging something as faint as the Earth would be impossible as the light from the Sun would blind the camera.

The problem is illustrated below.

Mars-Sun-Earth angles. Credit: ESA

Mars-Sun-Earth angles. Credit: ESA

So what we needed was some middle ground, a period where the angle is large enough such that a sufficient amount of Earth is illuminated, but not so large that the Sun is too close to the camera's field of view.

With the help of JPL's HORIZONS solar system ephemerides computation service we were able to work out that the solid angle of the illuminated fraction of Earth was at its maximum on 21 June this year. We then tried to find an observation opportunity as close to this date as possible.

To keep the Sun as far from the camera's field of view as possible, it was decided we would not aim to have the Earth in the centre of the image, but instead offset it by 10 degrees.

The solid angle of the illuminated fraction of the Earth was at its maximum on 21 June this year. Date via JPL Horizons. Credit: ESA

The solid angle of the illuminated fraction of the Earth was at its maximum on 21 June this year. Date via JPL Horizons. Credit: ESA

The next issue we encountered was the need to tell the spacecraft to point VMC at Earth.

On Mars Express, our instrument platform is fixed to the spacecraft, so to point our instruments at a particular spot we have to turn and point the entire spacecraft.

To determine where we point the spacecraft, first the instrument teams have to tell our Science Planning team based at ESAC, in Spain, where they want their instruments to point and when. This is processed by the science planners and then sent here to ESOC to the Mars Express mission planning team.

Our mission planning system takes in all of the pointing requests that our science planners have sent, analyses them to check for critical factors like power consumption, illumination of the solar arrays and data generation as well as other constraints and requirements.

Screenshot: Mars Express mission planning system. Credit: ESA

Screen shot: Mars Express mission planning system. Credit: ESA

If all checks are OK, one of the outputs is a list containing an entire month's set of spacecraft pointings.

To fit in with this process, we generated a single new VMC 'Earth' pointing by using a software tool we developed ourselves. This new pointing was then added to the monthly list sent by the science planners and processed and checked by the mission planning system.

This set of spacecraft pointings is then sent off to the flight dynamics team here at ESOC. They are able to determine the spacecraft's exact position at any point in time.

Combining this information and knowledge of the spacecraft layout and the position of each instrument, they are able to calculate the orientation the spacecraft must have for it to point a specific instrument toward its desired target.

These calculations are performed for an entire month of observations, while checking that the pointings do not violate any safety constraints. Implementing, maintaining, enforcing and providing strict constraints protects delicate optics and sensors against the perils of excessive heating and over-illumination by the Sun.

As with all spacecraft pointings, our custom Earth pointing had to pass these strict tests for us to be permitted to attempt the observation.

After flight dynamics completed their analysis, the results were then returned back to mission planning, where they can be converted into sets of commands for the spacecraft's attitude and orbit control system.

Once these commands are generated they are checked by the mission planners and the flight control team before being uplinked to Mars Express (once per week).

At this point, the observation has been scheduled, the pointing commands have been generated and checked and up-linked to the spacecraft and the final stage was to then create the command sequence to operate the camera.

This involves telling it when to switch on, how many images to take, the exposure settings to use and when to switch off – and to tell the on-board computer to generate a report of the amount of data the observation produced to enable us to keep track of the volume of stored data on board the spacecraft.

As we expected Earth to be faint, and to maximise our chances of getting a decent image, we decided to use the same settings as our Jupiter pictures, as they contained a wide range exposures from 30 seconds down to 2 seconds.

VMC Earth observation commands in the Mars Express mission control system. Credit: ESA

VMC Earth observation commands in the Mars Express mission control system. Credit: ESA

Once this is all on board the spacecraft, we then have to wait until the images are taken and then down-linked, where we can then run them through our processing tools.

So after all that, here it is.. the Earth, at a distance of 150 031 705 km taken on 3 July 2014 at 15:52 CET from orbit around Mars.

Earth seen from Mars. Credit: ESA/Mars Express/VMC

Earth seen from Mars. Credit: ESA/Mars Express/VMC

The bright patches you can see are sunlight hitting the top of the recess VMC sits in and then being reflected off the camera lens.

However, on the 2-second exposure, this glare is reduced sufficiently to leave Earth clearly visible in the middle left of the image (Note: the colours here are the result of the processing tool we run the VMC images through).

At first glance it doesn't look like a particularly exciting photo. Some lens flare and a small faint dot are visible.

Earth seen from Mars. Credit: ESA/Mars Express/VMC

Earth seen from Mars. Credit: ESA/Mars Express/VMC

However, remember: there are 7 billion people living on that small faint dot!

This quote from Carl Sagan describing the famous Voyager 1 photo 'pale blue dot' sums it up rather nicely:

Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every 'superstar,' every 'supreme leader,' every saint and sinner in the history of our species lived there.

As usual, these images along with every other photo VMC has taken are available on our flickr channel.

Editor's note: Thanks to Simon Wood and the entire MEX team for these excellent images and report.

 

Mars seen today

Excellent views of Mars acquired by the VMC today at 07:00 CEST (05:00 UTC), and downloaded within hours, transmitted to ESOC in Darmstadt, processed by the Mars Express team and... here it is! Thanks to the MEX team and Simon Wood.

Mars at 08:00 CEST today, with the MER-B landing site annotated. Credit: ESA/Mars Express/VMC

Mars at 07:00 CEST today, with the MER-B landing site annotated. Credit: ESA/Mars Express/VMC

Hot on the heels of yesterday's images, here are today's set fresh off the spacecraft; again we see possible clouds/dust round the poles.

These images were taken at an altitude of 9900 km above the surface at 07:00 CEST (5:00 UTC) this morning and transmitted back to Earth at 13:15 CEST (11:15 UTC).

This rapid turn around is in part due to the current Earth - Mars distance being 'only' 123 336 112 km. At this distance it only takes 6 mins 51 seconds for signals travel from the spacecraft to Earth. (As we get further away this can increase to up to 25 minutes.)

One-way light timePropagation delay display on the Mars Express Mission Control System

This proximity gives us higher data transmission rates, which mean we can transmit more of the stored data from the science instruments – and thus occasionally leaves us with spare data downlink capacity in some of our ground station passes. This spare capacity enables us to schedule the VMC data dumps much closer to the VMC observations.

Continuing from yesterday's highlighting of the Phoenix lander, here we have marked the landing site of the NASA Mars Exploration Rover B - Opportunity.

Opportunity is a fellow seasoned Martian explorer; it was launched only 5 days after Mars Express on 7 June 2003, landing on 25 January 2004 – one month after we entered Martian orbit.

This false-colour image of the interior of 'Endurance Crater' on Mars was collected on 4 August 2004 by NASA's Mars Exploration Rover Opportunity. It was relayed to Earth via ESA's Mars Express. The image, taken with the Rover's panoramic camera, was relayed to Earth by ESA's Mars Express together with other scientific data. Three separate frames, taken through red, green and blue filters, were combined to produce this colour image. NASA/JPL/Cornell

This false-colour image of the interior of 'Endurance Crater' on Mars was collected on 4 August 2004 by NASA's Mars Exploration Rover Opportunity. It was relayed to Earth via ESA's Mars Express. The image, taken with the Rover's panoramic camera, was relayed to Earth by ESA's Mars Express together with other scientific data. Three separate frames, taken through red, green and blue filters, were combined to produce this colour image. NASA/JPL/Cornell

Its landing site is located in the Meridiani Planum, an area of interest due to concentrations of the mineral Hematite, which on Earth is often formed in the presence of water.

With the possibility of water-formed minerals located here, it is not surprising that this is an area also investigated by our mineralogical Spectrometer OMEGA and our high resolution camera HRSC.

As with Phoenix, its sister rover Spirit and, currently, Curiosity, Mars Express has performed communication activities with Opportunity over the years, including the relay of the image above from the surface back to Earth.

As usual, the full set of this morning's images is available in Flickr.

 

Mars webcam spots Phobos

It’s been quiet on the VMC front over the last few months, but the good news is that our next VMC observation is scheduled for mid-May. However, don't think we haven't been busy behind the scenes in the meantime!

celestia_VMC_FRAME_MODE_TEST_2013-269In the summer of 2013, with the prospect of comets ISON and Siding Spring passing by Mars over the next 12 months, we wanted to have the ability to image them with VMC (if we got the opportunity). VMC has two operating modes: line mode and frame mode; the main difference between these is the image exposure times that can be set.

Line mode gives a maximum exposure of 200 millisseconds, and frame mode ranges from 200 milliseconds up to 95 seconds. The original on-board control procedure (i.e software commands) that operates VMC was only able to use line mode. This was a deliberate decision when the procedure was created to keep it as simple as possible, and 200ms is more than adequate for taking pictures of a well-illuminated Martian surface.

However, attempting to capture something as faint as a comet with a 200ms exposure on a 640x480 camera with no fancy optics was clearly going to be impossible. Thus the team decided this would be a good opportunity to perform a software upgrade that would enable us to operate VMC in both modes. Following a redesign of the algorithm, recoding and a period of validation against the spacecraft simulator, the upgraded procedure was uploaded to Mars Express. Once on board, the final step was to use it operationally.

A set of test images would be have to be taken and for this we needed a suitable target. The target had to be something bright enough that we stood a chance of imaging it but faint enough that we would likely be unable to see it on a short exposure. This was tricky given the limited number of test opportunities we had, but to our surprise and delight we discovered that Mars moon Phobos would pass through our field of view during the last of the slots we had identified .

Given that the last time long exposures were used on VMC was in 2007 (then just as a test to check it still worked) we had little information to go on regarding what exposure settings to use. The choice was further complicated by only having enough time to take 3 images.

In the end we decided on a large spread with 13-second, 6-second and 2-second exposures, as these would give us a good chance of capturing Phobos whilst also allowing us to assess the performance of the camera.

It was a tense wait to get the images back and see if all our work had paid off. Turned out we needn't have worried: not only had the upgraded software worked perfectly, but VMC had taken its first direct images of Phobos! We were absolutely thrilled with the results.

(13 seconds) 13-269_04.49.06_VMC_Img_No_2 (6 seconds) 13-269_04.50.01_VMC_Img_No_3

(2 seconds) 13-269_04.50.51_VMC_Img_No_4We estimate that we were approximately 8000 km away from Phobos when the images were taken (the increase in size/brightness is due to the different exposure times used). The 13-second and the 6-second images are a little over exposed (the glow in the bottom of the images is the light from the day side of Mars). In the final image (a 2-second exposure)  it is possible to get some indication of the overall shape of the Martian moon. Putting all images together in an animation, Phobos can be seen moving across the field of view.

phobosUnfortunately, our follow up observation of ISON did not go as well as we'd hoped. In the end, it was not as bright as originally expected and simply too faint to detect even with longer exposure times. All was not lost though, as we were left with these great shots of Phobos and new and proven imaging opportunities for VMC!

– MEX Team

Mars Full Orbit Video 2.0: Kepler rocks the Red Planet

Just in time to celebrate the 10th anniversary of Mars Express: a new and enhanced Full Orbit Video delivered by the VMC camera - the Mars Webcam!

The version below is a special 'MEX birthday preview' – we'll post a somewhat extended version late next week (along with a more detailed explanation on how this video was produced), to coincide with the next expected VMC image set arriving from Mars.

What's the 'Full Orbit video', you ask? Access the original FO video produced in 2010 for the full description.

Thanks to the Mars Express Science & Operations teams for generating a fabulous, unique-in-our-Solar-System view of the Red Planet.

Happy Birthday, Mars Express!