The "ocean worlds" of the Solar System. Credit: NASA/JPL
Within our Solar Systems, there are several moons where astronomers believe life could be found. This includes Ceres, Callisto, Europa, Ganymede, Enceladus, Titan, and maybe Dione, Mimas, Triton, and the dwarf planet Pluto. These “ocean worlds” are believed to have abundant liquid water in their interiors, as well as organic molecules and tidal heating – the basic ingredients for life.
Which raises the all-important question: are similar moons to be found in other star systems? This is the question NASA planetary scientist Dr. Lynnae C. Quick and her team from NASA’s Goddard Space Flight Center sought to address. In a recent study, Quick and her colleagues examined a sample of exoplanet systems and found that ocean worlds are likely to be very common in our galaxy.
This is the first glimpse of JUICE's eventual destination captured by the spacecraft's NavCam during ground testing. Image Credit: Airbus Defense and Space.
Is there a more complicated and sophisticated technological engineering project than a spacecraft? Maybe a particle accelerator or a fusion power project. But other than those two, the answer is probably no.
Spacecraft like the ESA’s JUICE don’t just pop out of the lab ready to go. Each spacecraft like JUICE is a singular design, and they require years—or even a decade or more—of work before they ever see a launch pad. With a scheduled launch date of 2022, JUICE is in the middle of all that work. Now its cameras are capturing images of Jupiter and its icy moons as part of its navigation calibration and fine-tuning.
“It felt particularly meaningful to conduct our tests already on our destination!”
Gregory Jonniaux, Vision-Based Navigation expert at Airbus Defence and Space.
Welcome to the 583rd Carnival of Space! The Carnival is a community of space science and astronomy writers and bloggers, who submit their best work each week for your benefit. We have a fantastic roundup today so now, on to this week’s worth of stories! Continue reading “Carnival of Space #583”
Jupiter's moon Ganymede, the largest moon in the Solar System, seen orbiting Jupiter, the largest planet in the Solar System. This image was taken by the Cassini spacecraft. Image Credit: NASA/JPL/University of Arizona
Ganymede was shaped by pronounced periods of tectonic activity in the past, according to a new paper. It’s no longer active and its surface is more-or-less frozen in place now. But this discovery opens the door to better planning for future missions to Jupiter’s other frozen moon Europa. Unlike Ganymede, Europa is still tectonically active, and understanding past geological activity on Ganymede helps us understand present-day Europa.
The Juno Infrared Auroral Mapper (JIRAM) captured this infrared image of Jupiter's south pole. This part of Jupiter cannot be seen from Earth. Image: NASA/JPL-Caltech/SwRI/MSSS
Since it arrived in orbit around Jupiter in July of 2016, the Juno mission has been sending back vital information about the gas giant’s atmosphere, magnetic field and weather patterns. With every passing orbit – known as perijoves, which take place every 53 days – the probe has revealed things about Jupiter that scientists will rely on to learn more about its formation and evolution.
Interestingly, some of the most recent information to come from the mission involves how two of its moons affect one of Jupiter’s most interesting atmospheric phenomenon. As they revealed in a recent study, an international team of researchers discovered how Io and Ganymede leave “footprints” in the planet’s aurorae. These findings could help astronomers to better understand both the planet and its moons.
Infrared images obtained by the Cassini probe, showing disturbances in Jupiter’s aurorae caused by Io and Ganymede. Credit: (c) Science (2018).
Much like aurorae here on Earth, Jupiter’s aurorae are produced in its upper atmosphere when high-energy electrons interact with the planet’s powerful magnetic field. However, as the Juno probe recently demonstrated using data gathered by Ultraviolet Spectrograph (UVS) and Jovian Energetic Particle Detector Instrument (JEDI), Jupiter’s magnetic field is significantly more powerful than anything we see on Earth.
In addition to reaching power levels 10 to 30 times greater than anything higher than what is experienced here on Earth (up to 400,000 electron volts), Jupiter’s norther and southern auroral storms also have oval-shaped disturbances that appear whenever Io and Ganymede pass close to the planet. As they explain in their study:
“A northern and a southern main auroral oval are visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street.”
A Von Kármán vortex street, a concept in fluid dynamics, is basically a repeating pattern of swirling vortices caused by a disturbance. In this case, the team found evidence of a vortex streaming for hundreds of kilometers when Io passed close to the planet, but which then disappeared as the moon moved farther away from the planet.
Reconstructed view of Jupiter’s northern lights through the filters of the Juno Ultraviolet Imaging Spectrograph instrument on Dec. 11, 2016, as the Juno spacecraft approached Jupiter, passed over its poles, and plunged towards the equator. Credit: NASA/JPL-Caltech/Bertrand Bonfond
The team also found two spots in the auroral belt created by Ganymede, where the extended tail from the main auroral spots eventually split in two. While the team was not sure what causes this split, they venture that it could be caused by interaction between Ganymede and Jupiter’s magnetic field (since Ganymede is the only Jovian moon to have its own magnetic field).
These features, they claim, suggest that magnetic interactions between Jupiter and Ganymede are more complex than previously thought. They also indicate that neither of the footprints were where they expected to find them, which suggests that models of the planet’s magnetic interactions with its moons may be in need of revision.
Studying Jupiter’s magnetic storms is one of the primary goals of the Juno mission, as is learning more about the planet’s interior structure and how it has evolved over time. In so doing, astronomers hope to learn more about how the Solar System came to be. NASA also recently extended the mission to 2021, giving it three more years to gather data on these mysteries.
And be sure to enjoy this video of the Juno mission, courtesy of the Jet Propulsion Laboratory:
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
“Hitler’s acid” is a colloquial name used to refer to Orthocarbonic acid – a name which was inspired from the fact that the molecule’s appearance resembles a swastika. As chemical compounds go, it is quite exotic, and chemists are still not sure how to create it under laboratory conditions.
But it just so happens that this acid could exist in the interiors of planets like Uranus and Neptune. According to a recent study from a team of Russian chemists, the conditions inside Uranus and Neptune could be ideal for creating exotic molecular and polymeric compounds, and keeping them under stable conditions.
The study was produced by researchers from the Moscow Institute of Physics and Technology (MIPT) and the Skolkovo Institute of Science and Technology (Skoltech). Titled “Novel Stable Compounds in the C-H-O Ternary System at High Pressure”, the paper describes how the high pressure environments inside planets could create compounds that exist nowhere else in the Solar System.
Orthocarbonic acid (also known as Hitler’s acid). Credit: Moscow Institute of Physics and Technology
Professor Artem Oganov – a professor at Skoltech and the head of MIPT’s Computational Materials Discovery Lab – is the study’s lead author. Years back, he and a team of researchers developed the worlds most powerful algorithm for predicting the formation of crystal structures and chemical compounds under extreme conditions.
Known as the Universal Structure Predictor: Evolutionary Xtallography (UPSEX), scientists have since used this algorithm to predict the existence of substances that are considered impossible in classical chemistry, but which could exist where pressures and temperatures are high enough – i.e. the interior of a planet.
With the help of Gabriele Saleh, a postdoc member of MIPT and the co-author of the paper, the two decided to use the algorithm to study how the carbon-hydrogen-oxygen system would behave under high pressure. These elements are plentiful in our Solar System, and are the basis of organic chemistry.
Until now, it has not been clear how these elements behave when subjected to extremes of temperature and pressure. What they found was that under these types of extreme conditions, which are the norm inside gas giants, these elements form some truly exotic compounds.
Diagram of the interior structure of Uranus. Credit: Moscow Institute of Physics and Technology
“The smaller gas giants – Uranus and Neptune – consist largely of carbon, hydrogen and oxygen. We have found that at a pressure of several million atmospheres unexpected compounds should form in their interiors. The cores of these planets may largely consist of these exotic materials.”
Under normal pressure – i.e. what we experience here on Earth (100 kPa) – any carbon, hydrogen or oxygen compounds (with the exception of methane, water and CO²) are unstable. But at pressures in the range 1 to 400 GPa (10,000 to 4 million times Earth normal), they become stable enough to form several new substances.
These include carbonic acid, orthocarbonic acid (Hitler’s acid) and other rare compounds. This was a very unusual find, considering that these chemicals are unstable under normal pressure conditions. In carbonic acid’s case, it can only remain stable when kept at very low temperatures in a vacuum.
Diagram of the interior structure of Neptune. Credit: Moscow Institute of Physics and Technology
At pressures of 314 GPa, they determined that carbonic acid (H²CO³) would react with water to form orthocarbonic acid (H4CO4). This acid is also extremely unstable, and so far, scientists have not yet been able to produce it in a laboratory environment.
This research is of considerable importance when it comes to modelling the interior of planets like Uranus and Neptune. Like all gas giants, the structure and composition of their interiors have remained the subject of speculation due to their inaccessible nature. But it could also have implications in the search for life beyond Earth.
According to Oganov and Saleh, the interiors of many moons that orbit gas giants (like Europa, Ganymede and Enceladus) also experience these types of pressure conditions. Knowing that these kinds of exotic compounds could exist in their interiors is likely to change what scientist’s think is going on under their icy surfaces.
“It was previously thought that the oceans in these satellites are in direct contact with the rocky core and a chemical reaction took place between them,” said Oganov. “Our study shows that the core should be ‘wrapped’ in a layer of crystallized carbonic acid, which means that a reaction between the core and the ocean would be impossible.”
Europa’s cracked, icy surface imaged by NASA’s Galileo spacecraft in 1998. Credit: NASA/JPL-Caltech/SETI
For some time, scientists have understood that at high temperatures and pressures, the properties of matter change pretty drastically. And while here on Earth, atmospheric pressure and temperatures are quite stable (just the way we like them!), the situation in the outer Solar System is much different.
By modelling what can occur under these conditions, and knowing what chemical buildings blocks are involved, we could be able to determine with a fair degree of confidence what the interior’s of inaccessible bodies are like. This will give us something to work with when the day comes (hopefully soon) that we can investigate them directly.
Who knows? In the coming years, a mission to Europa may find that the core-mantle boundary is not a habitable environment after all. Rather than a watery environment kept warm by hydrothermal activity, it might instead by a thick layer of chemical soup.
Then again, we may find that the interaction of these chemicals with geothermal energy could produce organic life that is even more exotic!
This color view from NASA's Juno spacecraft is made from some of the first images taken by JunoCam after the spacecraft entered orbit around Jupiter on July 4, 2016. Credits: NASA/JPL-Caltech/SwRI/MSSS
This color view from NASA’s Juno spacecraft is made from some of the first images taken by JunoCam after the spacecraft entered orbit around Jupiter on July 4, 2016. Credits: NASA/JPL-Caltech/SwRI/MSSS
NASA’s newly arrived Jovian orbiter Juno has transmitted its first imagery since reaching orbit last week on July 4 after swooping over Jupiter’s cloud tops and powering back up its package of state-of-the-art science instruments for unprecedented research into determining the origin of our solar systems biggest planet.
The ‘Galilean’ moons are annotated from left to right in the lead image.
Juno’s visible-light camera named JunoCam was turned on six days after Juno fired its main engine to slow down and be captured into orbit around Jupiter – the ‘King of the Planets’ following a nearly five year long interplanetary voyage from Earth.
The image was taken when Juno was 2.7 million miles (4.3 million kilometers) distant from Jupiter on July 10, at 10:30 a.m. PDT (1:30 p.m. EDT, 5:30 UTC), and traveling on the outbound leg of its initial 53.5-day capture orbit.
Juno came within only about 3000 miles of the cloud tops and passed through Jupiter’s extremely intense and hazardous radiation belts during orbital arrival over the north pole.
Illustration of NASA’s Juno spacecraft firing its main engine to slow down and go into orbit around Jupiter. Lockheed Martin built the Juno spacecraft for NASA’s Jet Propulsion Laboratory. Credit: NASA/Lockheed Martin
The newly released JunoCam image is visible proof that Juno survived the do-or-die orbital fireworks on America’s Independence Day that placed the baskeball-court sized probe into orbit around Jupiter – and is in excellent health to carry out its groundbreaking mission to elucidate Jupiter’s ‘Genesis.’
“This scene from JunoCam indicates it survived its first pass through Jupiter’s extreme radiation environment without any degradation and is ready to take on Jupiter,” said Scott Bolton, principal investigator from the Southwest Research Institute in San Antonio, in a statement.
“We can’t wait to see the first view of Jupiter’s poles.”
Within two days of the nerve wracking and fully automated 35-minute-long Jupiter Orbital Insertion (JOI) maneuver, the Juno engineering team begun powering up five of the probes science instruments on July 6.
Animation of Juno 14-day orbits starting in late 2016. Credits: NASA/JPL-Caltech
All nonessential instruments and systems had been powered down in the final days of Juno’s approach to Jupiter to ensure the maximum chances for success of the critical JOI engine firing.
“We had to turn all our beautiful instruments off to help ensure a successful Jupiter orbit insertion on July 4,” said Bolton.
“But next time around we will have our eyes and ears open. You can expect us to release some information about our findings around September 1.”
Juno resumed high data rate communications with Earth on July 5, the day after achieving orbit.
We can expect to see more JunoCam images taken during this first orbital path around the massive planet.
But the first high resolution images are still weeks away and will not be available until late August on the inbound leg when the spacecraft returns and swoops barely above the clouds.
“JunoCam will continue to take images as we go around in this first orbit,” said Candy Hansen, Juno co-investigator from the Planetary Science Institute, Tucson, Arizona, in a statement.
“The first high-resolution images of the planet will be taken on August 27 when Juno makes its next close pass to Jupiter.”
All of JunoCams images will be released to the public.
During a 20 month long science mission – entailing 37 orbits lasting 14 days each – the probe will plunge to within about 2,600 miles (4,100 kilometers) of the turbulent cloud tops.
It will collect unparalleled new data that will unveil the hidden inner secrets of Jupiter’s origin and evolution as it peers “beneath the obscuring cloud cover of Jupiter and study its auroras to learn more about the planet’s origins, structure, atmosphere and magnetosphere.”
The solar powered Juno spacecraft approached Jupiter over its north pole, affording an unprecedented perspective on the Jovian system – “which looks like a mini solar system” – as it flew through the giant planets intense radiation belts in ‘autopilot’ mode.
Juno is the first solar powered probe to explore Jupiter or any outer planet.
In the final weeks of the approach JunoCam captured dramatic views of Jupiter and all four of the Galilean Moons moons — Io, Europa, Ganymede and Callisto.
At the post JOI briefing on July 5, these were combined into a spectacular JunoCam time-lapse movie released by Bolton and NASA.
Watch and be mesmerized -“for humanity, our first real glimpse of celestial harmonic motion” says Bolton.
Video caption: NASA’s Juno spacecraft captured a unique time-lapse movie of the Galilean satellites in motion about Jupiter. The movie begins on June 12th with Juno 10 million miles from Jupiter, and ends on June 29th, 3 million miles distant. The innermost moon is volcanic Io; next in line is the ice-crusted ocean world Europa, followed by massive Ganymede, and finally, heavily cratered Callisto. Galileo observed these moons to change position with respect to Jupiter over the course of a few nights. From this observation he realized that the moons were orbiting mighty Jupiter, a truth that forever changed humanity’s understanding of our place in the cosmos. Earth was not the center of the Universe. For the first time in history, we look upon these moons as they orbit Jupiter and share in Galileo’s revelation. This is the motion of nature’s harmony. Credits: NASA/JPL-Caltech/MSSS
The $1.1 Billion Juno was launched on Aug. 5, 2011 from Cape Canaveral, Florida atop the most powerful version of the Atlas V rocket augmented by 5 solid rocket boosters and built by United Launch Alliance (ULA). That same Atlas V 551 version just launched MUOS-5 for the US Navy on June 24.
The Juno spacecraft was built by prime contractor Lockheed Martin in Denver.
The mission will end in February 2018 with an intentional death dive into the atmosphere to prevent any possibility of a collision with Europa, one of Jupiter’s moons that is a potential abode for life.
The last NASA spacecraft to orbit Jupiter was Galileo in 1995. It explored the Jovian system until 2003.
From Earth’s perspective, Jupiter was in conjunction with Earth’s Moon shortly after JOI during the first week in July.
Personally its thrilling to realize that an emissary from Earth is once again orbiting Jupiter after a 13 year long hiatus as seen in the authors image below – coincidentally taken the same day as JunoCam’s first image from orbit.
Juno, Jupiter and the Moon as seen from I-95 over Dunn, NC on July 10, 2016. Credit: Ken Kremer/kenkremer.com
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
Learn more about Juno at Jupiter, SpaceX CRS-9 rocket launch, ISS, ULA Atlas and Delta rockets, Orbital ATK Cygnus, Boeing, Space Taxis, Mars rovers, Orion, SLS, Antares, NASA missions and more at Ken’s upcoming outreach events:
July 15-18: “SpaceX launches to ISS on CRS-9, Juno at Jupiter, ULA Delta 4 Heavy spy satellite, SLS, Orion, Commercial crew, Curiosity explores Mars, Pluto and more,” Kennedy Space Center Quality Inn, Titusville, FL, evenings
NASA’s Juno probe captured the image data for this composite picture during its Earth flyby on Oct. 9 over Argentina, South America and the southern Atlantic Ocean. Raw imagery was reconstructed and aligned by Ken Kremer and Marco Di Lorenzo, and false-color blue has been added to the view taken by a near-infrared filter that is typically used to detect methane. Credit: NASA/JPL/SwRI/MSSS/Ken Kremer/Marco Di Lorenzo
This annotated color view of Jupiter and its four largest moons -- Io, Europa, Ganymede and Callisto -- was taken by the JunoCam camera on NASA's Juno spacecraft on June 21, 2016, at a distance of 6.8 million miles (10.9 million kilometers) from Jupiter. Image credit: NASA/JPL-Caltech/MSSS
This annotated color view of Jupiter and its four largest moons — Io, Europa, Ganymede and Callisto — was taken by the JunoCam camera on NASA’s Juno spacecraft on June 21, 2016, at a distance of 6.8 million miles (10.9 million kilometers) from Jupiter. Image credit: NASA/JPL-Caltech/MSSS
Now just 7 days out from a critical orbital insertion burn, NASA’s Jupiter-boundJuno orbiter is closing in fast on the massive gas giant. And as its coming into focus the spacecraft has begun snapping a series of beautiful images of the biggest planet and its biggest moons.
In a newly released color image snapped by the probes educational public outreach camera named Junocam, banded Jupiter dominates a spectacular scene that includes the giant planet’s four largest moons — Io, Europa, Ganymede and Callisto.
Junocam’s image of the approaching Jovian system was taken on June 21, 2016, at a distance of 6.8 million miles (10.9 million kilometers) and hints at the multitude of photos and science riches to come from Juno.
“Juno on Jupiter’s Doorstep,” says a NASA description. “And the alternating light and dark bands of the planet’s clouds are just beginning to come into view,” revealing its “distinctive swirling bands of orange, brown and white.”
This color view of Jupiter and its four largest moons — Io, Europa, Ganymede and Callisto — was taken by the JunoCam camera on NASA’s Juno spacecraft on June 21, 2016, at a distance of 6.8 million miles (10.9 million kilometers) from Jupiter. Image credit: NASA/JPL-Caltech/MSSS
Rather appropriately for an American space endeavor, the fate of the entire mission hinges on do or die ‘Independence Day’ fireworks.
On the evening of July 4, Juno must fire its main engine for 35 minutes.
The Joy of JOI – or Jupiter Orbit Insertion – will place NASA’s robotic explorer into a polar orbit around the gas giant.
The approach over the north pole is unlike earlier probes that approached from much lower latitudes nearer the equatorial zone, and thus provide a perspective unlike any other.
After a five-year and 2.8 Billion kilometer (1.7 Billion mile) outbound trek to the Jovian system and the largest planet in our solar system and an intervening Earth flyby speed boost, the moment of truth for Juno is now inexorably at hand.
This colorized composite shows more than half of Earth’s disk over the coast of Argentina and the South Atlantic Ocean as the Juno probe slingshotted by on Oct. 9, 2013 for a gravity assisted acceleration to Jupiter. The mosaic was assembled from raw images taken by the Junocam imager. Credit: NASA/JPL/SwRI/MSSS/Ken Kremer/Marco Di Lorenzo
And preparations are in full swing by the science and engineering team to ensure a spectacular Fourth of July fireworks display.
The team has been in contact with Juno 24/7 since June 11 and already uplinked the rocket firing parameters.
Signals traveling at the speed of light take 10 minutes to reach Earth.
The protective cover that shields Juno’s main engine from micrometeorites and interstellar dust was opened on June 20.
“And the software program that will command the spacecraft through the all-important rocket burn was uplinked,” says NASA.
The pressurization of the propulsion system is set for June 28.
“We have over five years of spaceflight experience and only 10 days to Jupiter orbit insertion,” said Rick Nybakken, Juno project manager from NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a statement.
“It is a great feeling to put all the interplanetary space in the rearview mirror and have the biggest planet in the solar system in our windshield.”
On the night of orbital insertion, Juno will fly within 2,900 miles (4,667 kilometers) of the Jovian cloud tops.
All instruments except those critical for the JOI insertion burn on July 4, will be tuned off on June 29. That includes shutting down Junocam.
“If it doesn’t help us get into orbit, it is shut down,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio.
“That is how critical this rocket burn is. And while we will not be getting images as we make our final approach to the planet, we have some interesting pictures of what Jupiter and its moons look like from five-plus million miles away.”
During a 20 month long science mission – entailing 37 orbits lasting 11 days each – the probe will plunge to within about 3000 miles of the turbulent cloud tops and collect unprecedented new data that will unveil the hidden inner secrets of Jupiter’s origin and evolution.
“Jupiter is the Rosetta Stone of our solar system,” says Bolton. “It is by far the oldest planet, contains more material than all the other planets, asteroids and comets combined and carries deep inside it the story of not only the solar system but of us. Juno is going there as our emissary — to interpret what Jupiter has to say.”
During the orbits, Juno will probe beneath the obscuring cloud cover of Jupiter and study its auroras to learn more about the planet’s origins, structure, atmosphere and magnetosphere.
Junocam has already taken some striking images during the Earth flyby gravity assist speed boost on Oct. 9, 2013.
For example the dazzling portrait of our Home Planet high over the South American coastline and the Atlantic Ocean.
For a hint of what’s to come, see our colorized Junocam mosaic of land, sea and swirling clouds, created by Ken Kremer and Marco Di Lorenzo.
NASA’s Juno probe captured the image data for this composite picture during its Earth flyby on Oct. 9 over Argentina, South America and the southern Atlantic Ocean. Raw imagery was reconstructed and aligned by Ken Kremer and Marco Di Lorenzo, and false-color blue has been added to the view taken by a near-infrared filter that is typically used to detect methane. Credit: NASA/JPL/SwRI/MSSS/Ken Kremer/Marco Di Lorenzo
As Juno sped over Argentina, South America and the South Atlantic Ocean it came within 347 miles (560 kilometers) of Earth’s surface.
During the flyby, the science team observed Earth using most of Juno’s nine science instruments since the slingshot also serves as an important dress rehearsal and key test of the spacecraft’s instruments, systems and flight operations teams.
Juno soars skyward to Jupiter on Aug. 5, 2011 from launch pad 41 at Cape Canaveral Air Force Station at 12:25 p.m. EDT. View from the VAB roof. Credit: Ken Kremer/kenkremer.com
Planets and other objects in our Solar System. Credit: NASA.
It is a well known fact that the planets of the Solar System vary considerably in terms of size. For instance, the planets of the inner Solar System are smaller and denser than the gas/ice giants of the outer Solar System. And in some cases, planets can actually be smaller than the largest moons. But a planet’s size is not necessarily proportional to its mass. In the end, how massive a planet is has more to do with its composition and density.
So while a planet like Mercury may be smaller in size than Jupiter’s moon Ganymede or Saturn’s moon Titan, it is more than twice as massive than they are. And while Jupiter is 318 times as massive as Earth, its composition and density mean that it is only 11.21 times Earth’s size. Let’s go over the planet’s one by one and see just how massive they are, shall we?
Mercury:
Mercury is the Solar System’s smallest planet, with an average diameter of 4879 km (3031.67 mi). It is also one of its densest at 5.427 g/cm3, which is second only to Earth. As a terrestrial planet, it is composed of silicate rock and minerals and is differentiated between an iron core and a silicate mantle and crust. But unlike its peers (Venus, Earth and Mars), it has an abnormally large metallic core relative to its crust and mantle.
All told, Mercury’s mass is approximately 0.330 x 1024 kg, which works out to 330,000,000 trillion metric tons (or the equivalent of 0.055 Earths). Combined with its density and size, Mercury has a surface gravity of 3.7 m/s² (or 0.38 g).
Internal structure of Mercury: 1. Crust: 100–300 km thick 2. Mantle: 600 km thick 3. Core: 1,800 km radius. Credit: MASA/JPL
Venus:
Venus, otherwise known as “Earth’s Sister Planet”, is so-named because of its similarities in composition, size, and mass to our own. Like Earth, Mercury and Mars, it is a terrestrial planet, and hence quite dense. In fact, with a density of 5.243 g/cm³, it is the third densest planet in the Solar System (behind Earth and Mercury). Its average radius is roughly 6,050 km (3759.3 mi), which is the equivalent of 0.95 Earths.
And when it comes to mass, the planet weighs in at a hefty 4.87 x 1024 kg, or 4,870,000,000 trillion metric tons. Not surprisingly, this is the equivalent of 0.815 Earths, making it the second most massive terrestrial planet in the Solar System. Combined with its density and size, this means that Venus also has comparable gravity to Earth – roughly 8.87 m/s², or 0.9 g.
Earth:
Like the other planets of the inner Solar System, Earth is also a terrestrial planet, composed of metals and silicate rocks differentiated between an iron core and a silicate mantle and crust. Of the terrestrial planets, it is the largest and densest, with an average radius of 6,371.0 km (3,958.8 mi) and a mean of density of 5.514 g/cm3.
The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
And at 5.97 x 1024 kg (which works out to 5,970,000,000,000 trillion metric tons) Earth is the most massive of all the terrestrial planets. Combined with its size and density, Earth experiences the surface gravity that we are all familiar with – 9.8 m/s², or 1 g.
Mars:
Mars is the third largest terrestrial planet, and the second smallest planet in our Solar System. Like the others, it is composed of metals and silicate rocks that are differentiated between a iron core and a silicate mantle and crust. But while it is roughly half the size of Earth (with a mean diameter of 6792 km, or 4220.35 mi), it is only one-tenth as massive.
In short, Mars has a mass of 0.642 x1024 kg, which works out to 642,000,000 trillion metric tons, or roughly 0.11 the mass of Earth. Combined with its size and density – 3.9335 g/cm³ (which is roughly 0.71 times that of Earth’s) – Mars has a surface gravity of 3.711 m/s² (or 0.376 g).
Jupiter:
Jupiter is the largest planet in the Solar System. With a mean diameter of 142,984 km, it is big enough to fit all the other planets (except Saturn) inside itself, and big enough to fit Earth 11.8 times over. But with a mass of 1898 x 1024 kg (or 1,898,000,000,000 trillion metric tons), Jupiter is more massive than all the other planets in the Solar System combined – 2.5 times more massive, to be exact.
Jupiter’s structure and composition. (Image Credit: Kelvinsong CC by S.A. 3.0)
However, as a gas giant, it has a lower overall density than the terrestrial planets. It’s mean density is 1.326 g/cm, but this increases considerably the further one ventures towards the core. And though Jupiter does not have a true surface, if one were to position themselves within its atmosphere where the pressure is the same as Earth’s at sea level (1 bar), they would experience a gravitational pull of 24.79 m/s2 (2.528 g).
Saturn:
Saturn is the second largest of the gas giants; with a mean diameter of 120,536 km, it is just slightly smaller than Jupiter. However, it is significantly less massive than its Jovian cousin, with a mass of 569 x 1024 kg (or 569,000,000,000 trillion metric tons). Still, this makes Saturn the second most-massive planet in the Solar System, with 95 times the mass of Earth.
Much like Jupiter, Saturn has a low mean density due to its composition. In fact, with an average density of 0.687 g/cm³, Saturn is the only planet in the Solar System that is less dense than water (1 g/cm³). But of course, like all gas giants, its density increases considerably the further one ventures towards the core. Combined with its size and mass, Saturn has a “surface” gravity that is just slightly higher than Earth’s – 10.44 m/s², or 1.065 g.
Diagram of Saturn’s interior. Credit: Kelvinsong/Wikipedia Commons
Uranus:
With a mean diameter of 51,118 km, Uranus is the third largest planet in the Solar System. But with a mass of 86.8 x 1024 kg (86,800,000,000 trillion metric tons) it is the fourth most massive – which is 14.5 times the mass of Earth. This is due to its mean density of 1.271 g/cm3, which is about three quarters of what Neptune’s is. Between its size, mass, and density, Uranus’ gravity works out to 8.69 m/s2, which is 0.886 g.
Neptune:
Neptune is significantly larger than Earth; at 49,528 km, it is about four times Earth’s size. And with a mass of 102 x 1024 kg (or 102,000,000,000 trillion metric tons) it is also more massive – about 17 times more to be exact. This makes Neptune the third most massive planet in the Solar System; while its density is the greatest of any gas giant (1.638 g/cm3). Combined, this works out to a “surface” gravity of 11.15 m/s2 (1.14 g).
As you can see, the planets of the Solar System range considerably in terms of mass. But when you factor in their variations in density, you can see how a planets mass is not always proportionate to its size. In short, while some planets may be a few times larger than others, they are can have many, many times more mass.
Surface features of the four members at different levels of zoom in each row
Continuing with our “Definitive Guide to Terraforming“, Universe Today is happy to present to our guide to terraforming Jupiter’s Moons. Much like terraforming the inner Solar System, it might be feasible someday. But should we?
Fans of Arthur C. Clarke may recall how in his novel, 2010: Odyssey Two (or the movie adaptation called 2010: The Year We Make Contact), an alien species turned Jupiter into a new star. In so doing, Jupiter’s moon Europa was permanently terraformed, as its icy surface melted, an atmosphere formed, and all the life living in the moon’s oceans began to emerge and thrive on the surface.
As we explained in a previous video (“Could Jupiter Become a Star“) turning Jupiter into a star is not exactly doable (not yet, anyway). However, there are several proposals on how we could go about transforming some of Jupiter’s moons in order to make them habitable by human beings. In short, it is possible that humans could terraform one of more of the Jovians to make it suitable for full-scale human settlement someday.
