Rugby 2018

Every year Rugby School hosts a day for physics teachers, which includes lectures and workshops.

Robotic Exploration of the Solar System

Prof. Emma Bunce, University of Leicester


On Thursday 7th of June I was lucky enough to attend this lecture. The following are my notes (and any mistakes are mine). I have taken images from the internet, which I will acknowledge, but if I am not allowed to use them don’t hesitate to let me know and I will remove them.

The missions have been involved in space physics. Some of the activities have been to investigate the electromagnetic environment and aurora of some of the planets.



Cassini-Huygens on the launch pad

Launched in 1997 it travelled 3.5 billion and carried a passenger to the Saturn system, the European Huygens probe—the first human-made object to land on a world in the distant outer solar system.

It took seven years to get to Saturn, arriving in 2004.

Animation of Cassini’s trajectory from 15 October 1997 to 4 May 2008


The Cassini space probe performed two gravitational-assist flybys of Venus on April 26, 1998, and June 24, 1999. These flybys provided the space probe with enough momentum to travel all the way out to the asteroid belt and reduced the quantity of fuel required. At that point, the Sun’s gravity pulled the space probe back into the inner Solar System.

On August 18, 1999, at 03:28 UTC, the craft made a gravitational-assist flyby of the Earth. One hour and 20 minutes before closest approach, Cassini made its closest approach to the Earth’s Moon at 377,000 kilometres, and it took a series of calibration photos.

On January 23, 2000, Cassini performed a flyby of the asteroid 2685 Masursky at around 10:00 UTC. It took photos in the period five to seven hours before the flyby at a distance of 1.6 million kilometres, and a diameter of 15 to 20 km was estimated for the asteroid.

Cassini made its closest approach to Jupiter on December 30, 2000, and made many scientific measurements. About 26,000 images of Jupiter, its faint rings, and its moons were taken during the six month flyby. It produced the most detailed global colour portrait of the planet yet, in which the smallest visible features are approximately 60 km across.


A Jupiter flyby picture

Cassini reached Saturn on the 30th June 2004.


Artist’s concept of Cassini’s orbit insertion around Saturn

Animation of Cassini’s trajectory around Saturn from 1 May 2004 to 7 August 2008


The mission ended on the 15th of September 2017. It completed 294 orbits and there were 162 targeted moon flybys.

The “Grand Finale” took place between 26th April to 15th September 2017 A final Titan flyby on April 22, 2017. Cassini’s orbit was changed to fly it through the gap between Saturn and its inner ring days late on April 26. Cassini passed about 3,100 km (1,900 mi) above Saturn’s cloud layer and 320 km from the visible edge of the inner ring; it successfully took images of Saturn’s atmosphere and began returning data the next day. After a further 22 orbits through the gap, the mission was ended with a dive into Saturn’s atmosphere on September 15; signal was lost at 7:55:46 AM EDT on September 15, 2017, just 30 seconds later than predicted. It is estimated that the spacecraft burned up about 45 seconds after the last transmission. The reason for its destruction was to ensure protection and prevent biological contamination to any of the moons of Saturn thought to offer potential habitability.

The mission of Cassini was to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA’s Cassini probe, and ESA’s Huygens lander which landed on Saturn’s largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.

The spacecraft operation was organized around a series of missions. Each is structured according to a certain amount of funding, goals, etc. At least 260 scientists from 17 countries have worked on the Cassini–Huygens mission; in addition thousands of people overall worked to design, manufacture, and launch the mission.

Prime Mission, July 2004 through June 2008.

Cassini Equinox Mission was a two-year mission extension which ran from July 2008 through September 2010.


Saturn reached equinox in 2008, shortly after the end of the prime mission.

Cassini Solstice Mission ran from October 2010 through April 2017. (Also known as the XXM mission.)

Grand Finale (spacecraft directed into Saturn), April 2017 to September 15, 2017.

A northern spring storm was seen on the 20th October 2011.

On October 25, 2012, Cassini witnessed the aftermath of the massive Great White Spot storm, 2000km across, which recurs roughly every 30 years on Saturn. Data from the composite infrared spectrometer (CIRS) instrument indicated a powerful discharge from the storm that caused a temperature spike in the stratosphere of Saturn 83 K above normal and showed a vortex hurricane.


Northern hemisphere storm in 2011

A shape in form of a hexagon can be seen 77 degrees North on Saturn. There is no southern counterpart. It was first spotted by Voyager and suggested a persistent feature.

Between 2012 and 2016, the persistent hexagonal cloud pattern at Saturn’s North Pole changed from a mostly blue colour to more of a golden colour. One theory for this is a seasonal change: extended exposure to sunlight may be creating haze as the pole swivels toward the sun. It was previously noted that there was less blue colour overall on Saturn between 2004 and 2008.


2013 and 2017: hexagon colour changes

The rings and small moons of Saturn would just fit between our Earth and our Moon.

In total, the Cassini mission discovered seven new moons orbiting Saturn. Using images taken by Cassini, researchers discovered Methone, Pallene and Polydeuces in 2004, although later analysis revealed that Voyager 2 had photographed Pallene in its 1981 flyby of the ringed planet.


On May 1, 2005, a new moon was discovered by Cassini in the Keeler gap. It was given the designation S/2005 S 1 before being named Daphnis. Its presence was indicated because of perturbations in the Keeler gap.


Discovery photograph of moon Daphnis

Pan and Prometheus are in a ring gap and steal materials from the rings.

Ice mountains can be seen in the rings.

Cassini had its first flyby of Saturn’s largest moon, Titan, on July 2, 2004, a day after orbit insertion, when it approached to within 339,000 km of Titan. Images taken through special filters (able to see through the moon’s global haze) showed south polar clouds thought to be composed of methane and surface features with widely differing brightness. On October 27, 2004, the spacecraft executed the first of the 45 planned close flybys of Titan when it passed a mere 1,200 kilometers above the moon. Almost four gigabits of data were collected and transmitted to Earth, including the first radar images of the moon’s haze-enshrouded surface. It revealed the surface of Titan (at least the area covered by radar) to be relatively level, with topography reaching no more than about 50 metres in altitude. The flyby provided a remarkable increase in imaging resolution over previous coverage. Images with up to 100 times better resolution were taken and are typical of resolutions planned for subsequent Titan flybys. Cassini collected pictures of Titan and the lakes of methane were similar to the lakes of Earth.


Huygens view of Titan’s surface (above left); Same image with different data processing (above right)

108 targeted flybys mapped 43% of Titan’s surface using radar imaging and identified 17 different molecules in the atmosphere. Seas and lakes of methane and ethane cover 20% of the surface.

Huygens was an atmospheric entry probe that landed successfully on Saturn’s moon Titan in 2005. Built and operated by the European Space Agency (ESA), it was part of the Cassini–Huygens mission and became the first spacecraft ever to land on Titan and the farthest landing from Earth a spacecraft has ever made. The probe was named after the Dutch 17th-century astronomer Christiaan Huygens, who discovered Titan in 1655.


Titan – infrared views (2004 – 2017)

Icy moons of Saturn include Dione and Thethys, which are heavily cratered.

Other moons:

Mimas is 400km across and has a crater called Herschel. It is jokingly called the Death Star, because it looks like the death star in Star Wars;


Hyperion’s surface has tiny craters;


Phoebe has an eccentric orbit. It could have been “captured” by Saturn;


Atlas is weird looking;


Enceladus is very bright and does not have its own magnetic field. Plumes of salty water can be seen escaping from its surface.


Saturn has a magnetic field similar to Earth’s.

The Hubble telescope has imaged Saturn’s aurora storms, which are caused by solar disturbances travelling through the solar system and compressing the magnetosphere.

Cassini’s magnetometer data showed that the magnetic field of Saturn rotates with planet itself and that Enceladus and the solar wind affects it.


Jupiter is a gas giant and the largest planet in the Solar System. In fact it makes up 2/3rd of the mass of planets in the Solar System.

It rotates once every 9.5 hours and has a dynamic atmosphere. The best known feature of Jupiter is the Great Red Spot, a persistent anticyclonic storm that is larger than Earth, located 22° south of the equator. It is known to have been in existence since at least 1831, and possibly since 1665. Images by the Hubble Space Telescope have shown as many as two “red spots” adjacent to the Great Red Spot. The storm is large enough to be visible through Earth-based telescopes with an aperture of 12 cm or larger. The oval object rotates counterclockwise, with a period of about six days. The maximum altitude of this storm is about 8 km above the surrounding cloudtops.


Great Red Spot is decreasing in size (May 15, 2014).

The video above shows a time-lapse sequence from the approach of Voyager 1. It shows the motion of atmospheric bands and the circulation of the Great Red Spot. It was recorded over 32 days with one photograph taken every 10 hours (once per Jovian day).

Jupiter has 60 different moons.

Juno is a NASA space probe orbiting the planet Jupiter. It was launched from Cape Canaveral Air Force Station on August 5, 2011 (UTC), as part of the New Frontiers program, and entered a polar orbit of Jupiter on July 5, 2016 (UTC), to begin a scientific investigation of the planet. After completing its mission, Juno will be intentionally deorbited into Jupiter’s atmosphere in 2021.

Juno’s highly elliptical initial polar orbit takes it within 4,200 kilometres of the planet and out to 8.1 million km, far beyond Callisto’s orbit.

It is expected to complete 12 science orbits before the end of its budgeted mission plan. The orbits were carefully planned in order to minimize contact with Jupiter’s dense radiation belts, which can damage spacecraft electronics and solar panels, by exploiting a gap in the radiation envelope near the planet, passing through a region of minimal radiation.

Artist’s rendering of the Juno spacecraft can be seen below


Juno’s mission is to measure Jupiter’s composition, gravity field, magnetic field, and polar magnetosphere. It will also search for clues about how the planet formed, including whether it has a rocky core, the amount of water present within the deep atmosphere, mass distribution, and its deep winds, which can reach speeds up to 618 kilometres per hour.

Jupiter’s aurora is the brightest in the Solar System. The main aurora is oval


Hubble image of the aurora

Scientists on NASA’s Juno mission have observed massive amounts of energy swirling over Jupiter’s polar regions that contribute to the giant planet’s powerful auroras – only not in ways the researchers expected.

Examining data collected by the ultraviolet spectrograph and energetic-particle detector instruments aboard the Jupiter-orbiting Juno spacecraft, a team led by Barry Mauk of the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, observed signatures of powerful electric potentials, aligned with Jupiter’s magnetic field, that accelerate electrons toward the Jovian atmosphere at energies up to 400,000 electron volts. This is 10 to 30 times higher than the largest auroral potentials observed at Earth, where only several thousands of volts are typically needed to generate the most intense auroras — known as discrete auroras — the dazzling, twisting, snake-like northern and southern lights seen in places like Alaska and Canada, northern Europe, and many other northern and southern polar regions.

The JUpiter ICy moons Explorer (JUICE) is an interplanetary spacecraft in development by the European Space Agency (ESA) with Airbus Defence and Space as the main contractor. The mission is being developed to visit the Jovian system focused on studying three of Jupiter’s Galilean moons: Ganymede, Callisto, and Europa (excluding the more volcanically active Io) all of which are thought to have significant bodies of liquid water beneath their surfaces, making them potentially habitable environments. The spacecraft is set for launch in June 2022 and would reach Jupiter in October 2029 after five gravity assists and 88 months of travel. By 2033 the spacecraft should enter orbit around Ganymede for its close up science mission and becoming the first spacecraft to orbit a moon other than the moon of Earth. The selection of this mission for the L1 launch slot of ESA’s Cosmic Vision science programme was announced on 2 May 2012. Its period of operations will overlap with NASA’s Europa Clipper mission, also launching in 2022.

Jupiter system has been picked because it is the archetype for the gas giants. It can be considered a Solar System in miniature. Ganymede and Callisto are actually bigger than Mercury.


In celestial mechanics, an orbital resonance occurs when orbiting bodies exert a regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Three of Jupiter’s Galilean moons, Ganymede, Europa and Io exhibit resonance. Squashes and pulls occur at their surfaces.

Io is the most volcanically active body. New Horizons flyby in 2007 caught eruptions. Io is also magnetically linked to Jupiter’s aurora.


Galileo mission discovered oceans on Europa. These oceans are thought to be up to 160km deep.


Ganymede is also thought to have underground oceans which could be up to 100km deep.


The oceans produce magnetic field signatures.

Bepicolombo – exploring Mercury


BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. The mission comprises two satellites to be launched together: the Mercury Planetary Orbiter (MPO) and Mio (Mercury Magnetospheric Orbiter, MMO). The mission will perform a comprehensive study of Mercury, including its magnetic field, magnetosphere, interior structure and surface. It is scheduled to launch in October 2018, with an arrival at Mercury (orbit insertion) planned for December 2025, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury. The mission was approved in November 2009, after years in proposal and planning as part of the European Space Agency’s Horizon 2000+ program; it will be the last mission of the program to be launched.

The University of Leicester designed and built the Mercury imaging X-ray spectrometer.

MIXS is in the test phase at the moment. There are ten other instruments in the science payload of the Mercury Planetary Orbiter besides MIXs.

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