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The Callisto satellite
image
Caption: Callisto is the outermost of the four large Galilean moons of Jupiter and the third largest in the whole solar system, falling behind only Ganymede and Saturn's moon Titan. It orbits Jupiter at an average distance of around 1.9 million kilometers, roughly six times the distance between Earth and the Moon.
With a diameter of nearly 5,000 kilometers, it is almost as large as Mercury, the smallest planet in our solar system, but has only a third of its mass as it is composed of approximately equal amounts of rock and ice.
Callisto orbits Jupiter in a tidally locked rotation, always showing the same side to Jupiter. In contrast to the other three Galilean satellites – Io, Europa, and Ganymede – it is not in orbital resonance due to its farther outward location and is thus not appreciably tidally heated. It does not show any signs of plate tectonics or volcanic activity. Its lack of geological processes means that surface features like craters remain unchanged for billions of years. It is thought to have evolved predominantly under the influence of impacts, as its surface is the oldest and most heavily cratered object in the solar system. In fact, it is so covered in craters that any new impact will likely erase a former one.
Callisto's internal structure is still subject to discussion; it may consist of a deep salty ocean. It is thought to be composed mainly of a mix of ice and rock, which are present in various states throughout the inner layers of the moon. Callisto hosts a very thin atmosphere composed mainly of carbon dioxide and some traces of oxygen. The moon has been studied by numerous space probes, such as the Pioneer and Voyager missions and the Galileo orbiter, and will be subject to further explorations by NASA, ESA, and China’s National Space Administration (CNSA).
Credit: NASA/JPL/DLR
Credit Link
Glossary Terms:
Galilean Satellites , Moons
License: Public Domain Public Domain icons
File
( image
610.45 kB)
Satellite swarm versus night sky beauty, by Torsten Hansen, Germany
image
Created for the OAE
Caption: Third place in the 2021 IAU OAE Astrophotography Contest, category Light pollution.
This image of Venus and the Pleiades also shows the tracks of the Starlink satellites. These satellites which are located at an altitude of approximately 550 kilometres, are part of an ever-growing constellation of satellites aimed to provide worldwide internet access. The reflective surfaces of the satellites, coupled with the fact that they are orbiting around the Earth, means that astronomical observations which require very long exposures capture “tracks” of the satellites in their images. Astronomical images used for scientific research are not usable because the measurements and data will contain these “tracks”. Because the number of satellites is expected to grow, it is likely that in the near future there will be no place on Earth where these satellites will not be visible crossing the sky. This is a new type of light pollution that seems to be an upcoming problem we will have to deal with, as these satellites might prevent optimal observation of the sky.
Credit: Torsten Hansen/IAU OAE
Glossary Terms:
Light Pollution , Artificial Satellite
License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons
This file on Zenodo ( image 5.66 MB)
Space debris orbiting the Earth
video
Caption: This animation shows objects orbiting the Earth. The data date from February 2024 and are taken from space-track.org which maintains a public catalogue of objects tracked by the United States Space Command (USSPACECOM).
At first in this video we see green dots, each representing one of the 31,000 human-made objects orbiting Earth. These include both operational and decommissioned satellites, used rocket stages from space launches, and fragments larger than 10cm created by collisions or explosions. Later in the video, some of the green dots are replace by orange dots, each of these representing one of the 9,300 operational satellites orbiting the Earth. Note that since February 2024 more satellites and rockets have been launched in to space and some objects will have fallen back to Earth, so these numbers will have changed.
We see two main groups of objects. The first are those objects orbiting close to the Earth, objects in low Earth orbit. These include communication satellites (many from the satellite constellations used to provide satellite internet services), Earth observation satellites, military satellites, two operational space stations and other objects such as rocket stages and other debris.
More distant from Earth we see a thin ring of satellites. These are in geostationary orbit. This is a special orbit where the orbital period matches the rotation period of the Earth. This means that a satellite in geostationary orbit stays above the same point on the equator and, when observed from the side of the Earth facing the satellite, will appear to stay at a position on the sky that does not change over time. Because of this, geostationary orbit is used by many communications satellites as a satellite dish on Earth used to receive or transmit a signal to that satellite can point in a fixed direction and does not need to dynamically track the satellite. Geostationary orbit is also used by weather observation satellites.
Credit: NASA's Scientific Visualization Studio
Credit Link
Glossary Terms:
Artificial Satellite , Space Debris , Spacecraft
Categories:
Planet Earth
, Space Exploration
License: Public Domain Public Domain icons
File
( video
18.61 MB)
Space debris orbiting the Earth
video
Caption: This animation shows objects orbiting the Earth. The data date from February 2024 and are taken from space-track.org which maintains a public catalogue of objects tracked by the United States Space Command (USSPACECOM).
At first in this video we see green dots, each representing one of the 31,000 human-made objects orbiting Earth. These include both operational and decommissioned satellites, used rocket stages from space launches, and fragments larger than 10cm created by collisions or explosions. Later in the video, some of the green dots are replace by orange dots, each of these representing one of the 9,300 operational satellites orbiting the Earth. Note that since February 2024 more satellites and rockets have been launched in to space and some objects will have fallen back to Earth, so these numbers will have changed.
We see two main groups of objects. The first are those objects orbiting close to the Earth, objects in low Earth orbit. These include communication satellites (many from the satellite constellations used to provide satellite internet services), Earth observation satellites, military satellites, two operational space stations and other objects such as rocket stages and other debris.
More distant from Earth we see a thin ring of satellites. These are in geostationary orbit. This is a special orbit where the orbital period matches the rotation period of the Earth. This means that a satellite in geostationary orbit stays above the same point on the equator and, when observed from the side of the Earth facing the satellite, will appear to stay at a position on the sky that does not change over time. Because of this, geostationary orbit is used by many communications satellites as a satellite dish on Earth used to receive or transmit a signal to that satellite can point in a fixed direction and does not need to dynamically track the satellite. Geostationary orbit is also used by weather observation satellites.
Credit: NASA's Scientific Visualization Studio
Credit Link
Glossary Terms:
Artificial Satellite , Space Debris , Spacecraft
Categories:
Planet Earth
, Space Exploration
License: Public Domain Public Domain icons
File
( video
18.61 MB)
Jupiter Moons Movie2, by Nicolas Hurez, Paul-Antoine Matrangolo, and Carl Pennypacker, United States of America
video
Created for the OAE
Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons.
This sequence shows the orbit of the four Galilean moons around the planet Jupiter. Almost two entire orbits of the innermost moon, Io, can be seen, with the other moons (Europa and Ganymede, but in particular Callisto) being further away, orbiting noticeably slower. The images were obtained in 2018 with the Las Cumbres Global Observatory at different locations on Earth, allowing a continuous sequence of images over approximately half a week without gaps during the day. With clear skies and over the course of several nights, the motion of the Galilean moons can also be observed with binoculars (ideally steady your elbows on a surface).
Credit: Nicolas Hurez, Paul-Antoine Matrangolo and Carl Pennypacker/IAU OAE
Glossary Terms:
Galilean Satellites , Gas Giant , Io , Jupiter , Moons , Orbit , Outer Planets , Planet
Categories:
Solar System
License: Creative Commons Attribution 4.0 International (CC BY 4.0) Creative Commons Attribution 4.0 International (CC BY 4.0) icons
This file on Zenodo ( video 890.47 kB)
