Using Martian Data

Oliver Blake

Using Martian Data - Curiosity Clock

• The Curiosity Clock app• Telling the time on Mars• Building the Gale Crater• Sunlight and shadows• The Martian sky• Viewing stars from Mars

The Curiosity Clock app

• Mars Science Laboratory (Curiosity Rover) landed in the Gale Crater in August 2012

• Operations on Mars are dictated by the day/night cycle, so calculations of time help with mission planning

• Using the time algorithms, and in conjunction with other available data, an Android app was created that gives a virtual view as seen from the rover

• App features are...

The Curiosity Clock appSols (Martian days)

since landingSolar Time (and current

displayed offset)

Position of the sun

Heading indicator Local terrain

Sky colour

Sunrise/set times

Telling the time on Mars

• The time format used for Mars missions is based on the solar day - a Martian day (or Sol) is 24.6 Earth hours long

• Local Mean Solar Time is a format where there are 24 hours in a Sol, but each Mars hour is slightly longer to allow for the longer day

• Mars time calculations are based on the paper :– “A post-Pathfinder evaluation of areocentric solar coordinates with improved timing recipes for

Mars seasonal/diurnal climate studies” by M Allison and M McEwen – Planetary and Space Science 48 (2000)

• A series of numerical recipes contained within calculate the position of Mars with relation to the sun for a given date, and with reference to the landing information (time and location) for a particular Mars lander, can be used to calculate the Sol number and solar time

• (Sol 0 is usually defined as starting at the local solar midnight on the landing day)

• As part of the calculation the sun’s position relative to the landing position is also worked out (more on this later)

Building the Gale Crater - Terrain

• The source data set – MOLA data from Mars Global Surveyor (launched 1996)

Building the Gale Crater - Terrain• MOLA data available for whole planet• Different levels of detail available

– Lowest 4 pixels per degree – 4 * 2MB raw image files– Highest 128 pixels per degree – 32 * 124MB files

• Need to balance level of detail with processing requirements

• Image shows sub-set of data used for Curiosity Clock app (brighter=higher)

• Raw image data and profile plotted with open source ImageJ software (not to scale vertically)

• In app, data is converted to a 3D polygon terrain model

Building the Gale Crater - Detail

• After creating 3D terrain model, image textures can be added to give more detail

• This image of the Gale Crater was taken by an orbiter (probably MGS MOC) and tinted with a generic Martian colour!

Comparison of app view with real view

• First panorama from Curiosity showing Mount Sharp (Aug 2012), and recreation from Curiosity Clock app

Sunlight and shadows• The sunlight and shadows are more a programming task, but using data from the first

two sources• The Mars time algorithm can also be used to calculate the azimuth and elevation of

the sun in the Martian sky• A shadow map is created by checking for any points on the terrain where a direct line

to the sun intersects with another point on the terrain• This images from the app show an aerial view of the Gale Crater, with some

shadowing visible from Mount Sharp, and a sun image with the size adjusted accordingly for the increased distance compared to earth

• There exist several sets of algorithms for calculating the sky colour on Earth, taking into account the suns position in the sky and atmospheric effects such as fog and haze.

• The basic effect is suitable for Mars – brighter as sun rises, bright in direction of sun etc.

• Main difference is sky colour (usually referred to as butterscotch)

The Martian sky

• Studies done of Mars sky colour using images from Spirit and Opportunity Rovers

• Other difference from Earth is blue sunsets (Spirit image)

2006

Viewing stars from Mars

• Roughly half the time (depending on season) app is used will be darkness – obvious answer to add interest was to add some stars

• Bright Stars Catalogue lists brightest 9110 stars as seen from Earth – position in sky, magnitude and colour

• Celestial sphere same for Mars – although offset due to different axial tilt – both angle and direction (pole stars etc. different)

• Drew the line at adding moons, Phobos and Deimos! (shapes, orbits etc)

VAUCOULEURS 1964

24 hours on Mars