Comet Siding Spring imaged by HRSC on board Mars Express

Comet Siding Spring came extraordinarily close to Mars as it whizzed by on 19 October 2014. The celestial body – a mere 500 metres in diameter – passed the Red Planet at a distance of just 137 000 kilometres, where it was observed by several spacecraft in orbit around Mars. The High Resolution Stereo Camera (HRSC), operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board ESA's Mars Express, also acquired a series of images with its SRC channel during Mars Express orbit 13710.

This animation combines multiple images that were acquired by the HRSC camera on board Mars Express during the comet Siding Spring flyby on 19 October 2014. Credit: ESA/DLR/FU Berlin

This animation combines multiple images that were acquired by the HRSC camera on board Mars Express during the comet Siding Spring flyby on 19 October 2014. Credit: ESA/DLR/FU Berlin

As it flew by, Siding Spring was travelling at a velocity of around 56 kilometres per second relative to Mars. Images were acquired at 17-second intervals; the spatial resolution is 17 kilometres per pixel. The images show the comet nucleus as well as the surrounding dust and gas cloud (coma).

Comet Siding Spring originates from the Oort Cloud, a comet ‘reservoir’ in the outer reaches of the Solar System. The comet was named after the Australian Observatory at which it was originally discovered back in 2013, and has the scientific designation C/2013 A1. As comets approach the Sun, one or two tails composed of gas and dust or ionised gases form on the side facing away from the Sun. As it whizzed by the planet, Siding Spring’s tail penetrated the Martian atmosphere, where it was analysed by the particle detector ASPERA-3 on board Mars Express, among others.

Scientists hope to use the data acquired, as well as the spectrometer measurements conducted at the same time, to gain an insight into the comet’s composition. It is thought that comets may contain material dating back to the formation of the Solar System.

Mars Express ready for comet Siding Spring

On 14 October at 16:18 CEST, Comet Siding Spring will be 25,001,331 km from the centre of Mars, 24,997,942 km from the surface of Mars (mean) and 24,997,399 km from Mars Express, closing at a speed of -55.88 km/second.

Comet C/2013 A1 Siding Spring seen on 6 September 2014 from Argentina. Image credit: César Nicolás Fornari https://www.facebook.com/cesar.fornari

Comet C/2013 A1 Siding Spring seen on 6 September 2014 from Argentina. Image credit: César Nicolás Fornari https://www.facebook.com/cesar.fornari

For the Comet Siding Spring encounter this weekend, the Mars Express mission team have decided to not execute the initial contingency plan of pointing the high gain antenna toward the expected direction of comet particles and switching off all non-essential systems. Instead, we will be taking advantage of this remarkable opportunity to perform science observations of the comet – yet with a few precautions.

Siding Spring will pass by Mars at 139 500 km – a little more than
1/3 the distance between Earth and our Moon.

The final decision was made at the beginning of October. As we had two plans ready – one dubbed 'nominal science' and one 'contingency' – we were able to make this decision close to the encounter date and take advantage of the latest estimates of comet activity.

In creating the weekly observation plan for the spacecraft, several teams and many different factors are involved. Not only do we have to decide on where to point the spacecraft but we also have to take into account the amount of data generated, ground station availability, power requirements, thermal conditions, pointing restrictions and several others. Each of these is a lot of work in itself and trying to have two plans that were as similar as possible kept our mission planning team quite busy. This is why we have to plan everything far in advance.

So, the plan we will use is much like our standard weekly operations, but with a few additional precautions:

  • NASA's DSN deep space tracking network are providing excellent support and will be allocating all of their antennas at both their Madrid and Goldstone sites purely to support the ESA, NASA and ISRO Mars missions. As well as using two of their 34m antennas to perform dumps of science data, we will be using the two giant 70m antennas to track a beacon signal that will be transmitted from one of the Mars Express low gain antennas (this was originally part of our contingency plan, but will be used in this now-routine science plan to give us an indication that all is well on the spacecraft).
  • We will also perform additional checks to the spacecraft systems. Once we get our first data after the comet encounter, engineers will go through all subsystems to be sure that everything is nominal and compare system status values to default values recorded earlier.
  • The Data Management Systems Engineers will dump all the data from our computer systems on Monday to be sure that nothing has become corrupted and our Power/Thermal Engineers will perform a test the week after flyby to measure any change in the performance of our solar arrays.

We are not expecting to find any problems but rather perform these tests so as to be sure.

MEX science during Siding Spring

Presentation by H. Svedhem, ESA's mission scientist for MEX, detailing the plans for science during Siding Spring flyby this week and next.

This presentation was given at the Comet Siding Spring (C/2013 A1) Science Workshop, NASA JPL, 19 September 2014.

The recording of the workshop features Hakan here:

From 1:17:00 to end

and

Until 18:29

Cosmic bully spotted by ESA and NASA

There are some great new Hubble images of our 'friend', Comet Siding Spring, due to pass by Mars at less than 136 000 km on 19 October – less than half the distance between Earth and our moon.

Comet Siding Spring imaged by ESA/NASA Hubble. Credit: NASA, ESA, and J.-Y. Li (Planetary Science Institute)

Comet Siding Spring imaged by ESA/NASA Hubble. Credit: NASA, ESA, and J.-Y. Li (Planetary Science Institute)

The passage of the comet may affect spacecraft in orbit around Mars, including ESA's Mars Express.

The image on the left above, captured 11 March by the NASA/ESA Hubble Space Telescope, shows comet C/2013 A1, also called Siding Spring, at a distance of 568 million km from Earth. Hubble can't see Siding Spring's icy nucleus because of its diminutive size. The nucleus is surrounded by a glowing dust cloud, or COMA, that measures roughly 19 000 km across.

The right image shows the comet after image processing techniques were applied to remove the hazy glow of the coma revealing what appear to be two jets of dust coming off the location of the nucleus in opposite directions. This observation should allow astronomers to measure the direction of the nucleus’s pole, and axis of rotation.

Hubble also observed Siding Spring on 21 January as Earth was crossing its orbital plane, which is the path the comet takes as it orbits the Sun. This positioning of the two bodies allowed astronomers to determine the speed of the dust coming off the nucleus.

"This is critical information that we need to determine whether, and to what degree, dust grains in the coma of the comet will impact Mars and spacecraft in the vicinity of Mars," said Jian-Yang Li of the Planetary Science Institute in Tucson, Arizona.

Compass and Scale Image for Comet C/2013 A1 Siding Spring (3 Epochs)

Compass and Scale Image for Comet C/2013 A1 Siding Spring (3 Epochs)
Source: Hubblesite.org

The image above shows a series of HST pictures of comet C/2013 A1 Siding Spring as observed on 29 October 2013, 21 January 2014 and 11 March 2014. The distances from Earth were, respectively, 605 million km, 552 million km, and 568 million km. The solid icy nucleus is too small to be resolved by Hubble, but it lies at the center of a dusty coma that is roughly 19 000 km across in these images.

When the glow of the coma is subtracted through image processing, which incorporates a smooth model of the coma's light distribution, Hubble resolves what appear to be two jets of dust coming off the nucleus in opposite directions. The jets have persisted through the three Hubble visits, with their directions in the sky nearly unchanged. These visible-light images were taken with Hubble's Wide Field Camera 3.

Discovered in January 2013 by Robert H. McNaught at Siding Spring Observatory, Australia, the comet is falling toward the Sun along a roughly 1-million-year orbit and is now within the radius of Jupiter's orbit. The comet will make its closest approach to our Sun on 25 October at a distance of 209 million km – well outside of Earth's orbit. The comet is not expected to become bright enough to be seen by the naked eye.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.