trojan asteroids

It’s International Asteroid Day!

There are more than 700,000 known asteroids, but how much do you know about these rocky remnants left over from the birth of our solar system 4.6 billion years ago? 

Today, June 30 is International Asteroid Day. Here are some things to know about our fascinating space rubble.

1. A Place in Space 

Asteroids—named by British astronomer William Herschel from the Greek expression meaning “star-like"—are rocky, airless worlds that are too small to be called planets. But what they might lack in size they certainly make up for in number: An estimated 1.1 to 1.9 million asteroids larger than 1 kilometer are in the Main Belt between the orbits of Mars and Jupiter. And there are millions more that are smaller in size. Asteroids range in size from Vesta—the largest at about 329 miles (529 kilometers) wide—to bodies that are just a few feet across.

2. What Lies Beneath 

Asteroids are generally categorized into three types: carbon-rich, silicate, or metallic, or some combination of the three. Why the different types? It all comes down to how far from the sun they formed. Some experienced high temperatures and partly melted, with iron sinking to the center and volcanic lava forced to the surface. The asteroid Vesta is one example we know of today.

3. Small Overall 

If all of the asteroids were combined into a ball, they would still be much smaller than the Earth’s moon.

4. Except for a Big One

In 1801, Giuseppe Piazzi discovered the first and then-largest asteroid, Ceres, orbiting between Mars and Jupiter. Ceres is so large that it encompasses about one-fourth of the estimated total mass of all the asteroids in the asteroid belt. In 2006, its classification changed from asteroid to  as a dwarf planet.

5. Mission to a Metal World 

NASA’s Psyche mission will launch in 2022 to explore an all-metal asteroid—what could be the core of an early planet—for the very first time. And in October 2021, the Lucy mission will be the first to visit Jupiter’s swarms of Trojan asteroids.

6. Near-Earth Asteroids

The term ‘near’ in near-Earth asteroid is actually a misnomer; most of these bodies do not come close to Earth at all. By definition, a near-Earth asteroid is an asteroid that comes within 28 million miles (44 million km) of Earth’s orbit. As of June 19, 2017, there are 16,209 known near-Earth asteroids, with 1,803 classified as potentially hazardous asteroids (those that could someday pose a threat to Earth).

7. Comin’ in Hot 

About once a year, a car-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface.

8. But We’re Keeping an Eye Out

Ground-based observatories and facilities such as Pan-STARRS, the Catalina Sky Survey, and ATLAS are constantly on the hunt to detect near-Earth asteroids. NASA also has a small infrared observatory in orbit about the Earth: NEOWISE. In addition to detecting asteroids and comets, NEOWISE also characterizes these small bodies.

9. Buddy System

Roughly one-sixth of the asteroid population have a small companion moon (some even have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.

10. Earthly Visitors 

Several NASA space missions have flown to and observed asteroids. The NEAR Shoemaker mission landed on asteroid Eros in 2001 and NASA’s Dawn mission was the first mission to orbit an asteroid in 2011. In 2005, the Japanese spacecraft Hayabusa landed on asteroid Itokawa. Currently, NASA’s OSIRIS-REx is en route to a near-Earth asteroid called Bennu; it will bring a small sample back to Earth for study.

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The planet Mars shares its orbit with a handful of small asteroids, the so-called Trojans. Among them, one finds a unique group, all moving in very similar orbits, suggesting that they originated from the same object. But the mechanism that produced this “family” has been a mystery. Now, an international team of astronomers believe they have identified the culprit: sunlight. Their findings, which highlight how small asteroids near the Sun may evolve, are to be presented at the annual Meeting of the Division for Planetary Sciences of the American Astronomical Society at Provo, Utah, this week, by Dr. Apostolos Christou, a Research Astronomer at the Armagh Observatory and Planetarium in Northern Ireland, United Kingdom, and leader of the research team.

Trojan asteroids are trapped within gravitational “safe havens” 60 degrees in front of and behind the planet. The point leading the planet is L4; that trailing the planet is L5. Mars is the only terrestrial planet known to have Trojan companions in stable orbits. The first Mars Trojan, discovered over 25 years ago at L5, was named “Eureka” in reference to the famous exclamation by ancient Greek mathematician Archimedes. The present tally is only 10, but even this relatively meager sample shows interesting structure not seen elsewhere.

For starters, all the Trojans, save one, are trailing Mars at its L5 Lagrange point. What’s more, the orbits of all but one of the L5 Trojans form a tight group, with 2-km sized Eureka its largest member and including objects as small as a few hundred meters.

The team have been working to determine how the family came to be. For instance, collisions that occurred hundreds of millions of years ago formed similar families in the asteroid belt between Mars and Jupiter. But an impact origin does not quite fit with what we know about these Trojans. As Christou points out: “This family is incredibly compact. Only the gentlest of impacts, with the fragments barely able to escape Eureka’s gravity, would work. Also, we know that the Yarkovsky effect, a tiny acceleration driven by absorbed and re-emitted sunlight on the asteroid, would cause family members to drift away over about a billion years. What our models show, instead, is that even impacts with just enough energy to break up Eureka are so rare that they may not happen over the age of the solar system.”

Taking a step back, the team then adopted a different approach, looking at the Martian Trojans as a whole instead of focusing on the family. From this perspective, the lack of a family around the two remaining Mars Trojans, (101429) 1998 VF31 at L5 and (121514) 1999 UJ7 at L4, becomes an important clue to this puzzle. Christou explains: “These two asteroids are at the same distance from the Sun and of similar size to Eureka, yet we don’t see asteroids grouping up near them. We believe this is telling us something about how families can or can’t form at Mars’s distance from the Sun.”

That “something” is very likely rotational fission, driven by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect – a sister effect to Yarkovsky & also driven by sunlight but changing the asteroid’s rotation rather than the orbit. This is causing Eureka to spin up, eventually spawning off pieces of itself that escape to become independent asteroids orbiting the Sun. Interestingly, Eureka rotates once every two-and-a-half hours, about as fast as an asteroid can spin without coming apart; and recently the team observed the L4 asteroid, 1999 UJ7, finding that it spins 20 times slower, or once every 2 days. Other slow-spinning asteroids of this size are found to be in a “tumbling” state where – at least in theory – YORP may “switch off.” UJ7 may, therefore, be simply incapable of producing new asteroids through fission.

This explanation, however, does not work for 1998 VF31, the remaining Trojan at L5, which the team found to rotate once every 8 hours, not slow enough to prevent YORP from spinning it up to the point of fission. But since we don’t see the new asteroids, something must be happening to them after they leave VF31. To find out what, Christou ran a computer simulation, following the orbits of virtual asteroids or clones produced by both VF31 and Eureka under the Yarkovsky effect. He discovered that, whereas Eureka “offspring” survive at L5 for more than a billion years, VF31 is sitting next to a dynamical “escape hatch” allowing any bits breaking off it to escape within only 200 to 300 million years. So, akin to water draining out of an unplugged washbasin, objects separating from VF31 would escape quickly, leaving its vicinity clear of asteroids. The result: no family.

Given the evidence in hand the fission hypothesis appears compelling, but Christou
cautions that this is far from a closed-and-shut case; only time and more work will tell if the conclusion is correct. To test their theory, they plan to look for fainter Trojans, 100 metres across or less. “We don’t currently see those, but a dedicated survey should detect them. Finding many small Trojans near Eureka, perhaps a few near VF31 but none at UJ7 would strongly indicate that we got it right.”

Ultimately, the work may have implications well beyond the solving of this little puzzle. Close to the Sun, YORP-induced fission – essentially the action of sunlight – may be as important for driving asteroid evolution as collisions. Indeed, Christou speculates that, if any stable Trojans of our own planet exist, YORP may turn them into a source of new near-Earth objects. “But that’s another story,” he concludes.

Trojan Asteroids:

Not all the asteroids in the solar system are from the asteroid belt, there are other clusters of asteroids in different orbits.

One of these clusters (or rather, two) are the Trojan asteroids. They orbit at roughly 60 degrees out of phase with Jupiter, but have the exact same orbital period/velocity - this is due to the fact that they occupy Lagrangian points - points at which Jupiter gravitational pull interacts with the suns gravitational pull in a precise way which allows a stable orbit. (Read more. no seriously, read more. It’s really interesting)

An interesting fact that i love about these asteroids (as a fan of science And history) is their naming: They are, obviously, named after the legendary siege of troy, But more than that - the group that are 60 degrees ahead of Jupiter are called the “Greeks” or the “Greek Camp” and the group that lie behind Jupiter are called the “Trojans” or the “Trojan Camp." Likewise each note-worthy asteroid discovered is named after the characters in the war, in each side respectively. 

Solar System: Things to Know This Week

We love Lucy—our spacecraft that will visit the ancient Trojan asteroids near Jupiter, that is. This week, let us count the ways this 2021 mission could revolutionize what we know about the origins of Earth and ourselves.

1. Lucky Lucy 

Earlier this year, we selected the Lucy mission to make the first-ever visit to a group of asteroids known as the Trojans. This swarm of asteroids orbits in two loose groups around the Sun, with one group always ahead of Jupiter in its path, and the other always behind. The bodies are stabilized by the Sun and Jupiter in a gravitational balancing act, gathering in locations known as Lagrange points.

2. Old. Really, Really Old

Jupiter’s swarms of Trojan asteroids may be remnants of the material that formed our outer planets more than 4 billion years ago—so these fossils may help reveal our most distant origins. “They hold vital clues to deciphering the history of the solar system,” said Dr. Harold F. Levison, Lucy principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado.

3. A Link to The Beatles

Lucy takes its name from the fossilized human ancestor, called “Lucy” by her discoverers, whose skeleton provided unique insight into humanity’s evolution. On the night it was discovered in 1974, the team’s celebration included dancing and singing to The Beatles’ song “Lucy In The Sky With Diamonds.” At some point during that evening, expedition member Pamela Alderman named the skeleton “Lucy,” and the name stuck. Jump ahead to 2013 and the mission’s principal investigator, Dr. Levison, was inspired by that link to our beginnings to name the spacecraft after Lucy the fossil. The connection to The Beatles’ song was just icing on the cake.

4. Travel Itinerary

One of two missions selected in a highly competitive process, Lucy will launch in October 2021. With boosts from Earth’s gravity, it will complete a 12-year journey to seven different asteroids: a Main Belt asteroid and six Trojans.

5. Making History

No other space mission in history has been launched to as many different destinations in independent orbits around the Sun. Lucy will show us, for the first time, the diversity of the primordial bodies that built the planets.

6. What Lies Beneath 

Lucy’s complex path will take it to both clusters of Trojans and give us our first close-up view of all three major types of bodies in the swarms (so-called C-, P- and D-types). The dark-red P- and D-type Trojans resemble those found in the Kuiper Belt of icy bodies that extends beyond the orbit of Neptune. The C-types are found mostly in the outer parts of the Main Belt of asteroids, between the orbits of Mars and Jupiter. All of the Trojans are thought to be abundant in dark carbon compounds. Below an insulating blanket of dust, they are probably rich in water and other volatile substances.

7. Pretzel, Anyone?

This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a slowly turning frame of reference that makes Jupiter appear stationary, giving the trajectory its pretzel-like shape.

8. Moving Targets

This time-lapsed animation shows the movements of the inner planets (Mercury, brown; Venus, white; Earth, blue; Mars, red), Jupiter (orange), and the two Trojan swarms (green) during the course of the Lucy mission.

9. Long To-Do List

Lucy and its impressive suite of remote-sensing instruments will study the geology, surface composition, and physical properties of the Trojans at close range. The payload includes three imaging and mapping instruments, including a color imaging and infrared mapping spectrometer and a thermal infrared spectrometer. Lucy also will perform radio science investigations using its telecommunications system to determine the masses and densities of the Trojan targets.

10. Dream Team

Several institutions will come together to successfully pull off this mission. The Southwest Research Institute in Boulder, Colorado, is the principal investigator institution. Our Goddard Space Flight Center will provide overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space Systems in Denver will build the spacecraft. Instruments will be provided by Goddard, the Johns Hopkins Applied Physics Laboratory and Arizona State University. Discovery missions are overseen by the Planetary Missions Program Office at our Marshall Space Flight Center in Huntsville, Alabama, for our Planetary Science Division.

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From a distance of 418 million miles, NASA’s OSIRIS-REx spacecraft took an image of Jupiter February 12. It marked the first long-range target for the PolyCam instrument, which is a narrow-field, long-range camera onboard the spacecraft. Two images were combined to create the image, one showing detail on Jupiter and one at a much higher exposure to capture three of the planet’s largest moons. From left to right are Callisto, Io, and Ganymede.

In an interesting comparison between the spacecraft’s different cameras, the wide-angle, short-range NavCam took the same image immediately after the above one. Jupiter and its moons appear as white, pixelated shapes with no discernable detail.

Both images were taken during the mission’s search for Earth-Trojan asteroids, bodies of rock that orbit the sun in an orbit of similar length and shape to Earth’s.

OSIRIS-REx, which launched September 8, 2016, was 76 million miles away from Earth at the time the image was taken. The spacecraft will swing by Earth in September 2017 for a gravity assist before reaching the asteroid Bennu in mid-2018.

OSIRIS-REx’s position when it took its photograph of Jupiter is shown below. The positions of Earth, Bennu, and Jupiter is also shown, as are some key milestones in the pre-arrival phase of the mission.


Solar System: Things to Know This Week

Our Psyche mission to a metal world, which will explore a giant metal asteroid known as 16 Psyche, is getting a new, earlier launch date. Psyche is now expected to launch from the Kennedy Space Center in 2022, cruise through the solar system for 4.6 years, and arrive at the Psyche asteroid in 2026, four years earlier than planned. 

Below are 10 things to know about this mission to a completely new and unexplored type of world.

1. Psyche, Squared 

Psyche is the name of the NASA space mission and the name of the unique metal asteroid orbiting the sun between Mars and Jupiter. The asteroid was discovered in 1852 by Italian astronomer Annibale de Gasparis and named after the Greek mythological figure Psyche, whom Cupid fell in love with. “Psyche” in Greek also means “soul.”

2. Mission: Accepted

The Psyche Mission was selected for flight earlier this year under NASA’s Discovery Program. And it will take a village to pull off: The spacecraft is being built by Space Systems Loral in Palo Alto, California; the mission is led by Arizona State University; and NASA’s Jet Propulsion Laboratory will be responsible for mission management, operations and navigation.

3. An Unusual Asteroid 

For the very first time, this mission will let us examine a world made not of rock and ice, but metal. Scientists think Psyche is comprised mostly of metallic iron and nickel, similar to Earth’s core - which means Psyche could be an exposed core of an early planet as large as Mars.

4. Sweet 16 

Psyche the asteroid is officially known as 16 Psyche, since it was the 16th asteroid to be discovered. It lies within the asteroid belt, is irregularly shaped, about the size of Massachusetts, and is about three times farther away from the sun than Earth.

5. Discoveries Abound 

The Psyche mission will observe the asteroid for 20 months. Scientists hope to discover whether Psyche is the core of an early planet, how old it is, whether it formed in similar ways to Earth’s core, and what its surface is like. The mission will also help scientists understand how planets and other bodies separated into their layers including cores, mantles and crusts early in their histories. “Psyche is the only known object of its kind in the solar system and this is the only way humans will ever visit a core,” said Principal Investigator Lindy Elkins-Tanton of Arizona State University.

6. Think Fast 

The mission launch and arrival were moved up because Psyche’s mission design team were able to plot a more efficient trajectory that no longer calls for an Earth gravity assist, ultimately shortening the cruise time. The new trajectory also stays farther from the sun, reducing the amount of heat protection needed for the spacecraft, and will still include a Mars flyby in 2023.

7. Gadgets Galore

The Psyche spacecraft will be decked out with a multispectral imager, gamma ray and neutron spectrometer, magnetometer, and X-band gravity science investigation. More:

8. Stunning Solar Panels 

In order to support the new mission trajectory, the solar array system was redesigned from a four-panel array in a straight row on either side of the spacecraft to a more powerful five-panel x-shaped design, commonly used for missions requiring more capability. Much like a sports car, combining a relatively small spacecraft body with a very high-power solar array design means the Psyche spacecraft will be able to speed to its destination much faster. Check out this artist’s-concept illustration here:

9. See For Yourself

Watch the planned Psyche mission in action.

10. Even More Asteroids

Our missions to asteroids began with the orbiter NEAR of asteroid Eros, which arrived in 2000, and continues with Dawn, which orbited Vesta and is now in an extended mission at Ceres. The mission OSIRIS-REx, which launched on Sept. 8, 2016, is speeding toward a 2018 rendezvous with the asteroid Bennu, and will deliver a sample back to Earth in 2023. The Lucy mission is scheduled to launch in October 2021 and will explore six Jupiter Trojan asteroids. More:

Want to learn more? Read our full list of the 10 things to know this week about the solar system HERE.

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“…and there among the dust did the blood, bones, and sinews of another brave crew join that dust. For an instant their fate was as another small star in the heavens, visible to few upon the Earth and of unclear import to those who noticed.” -EF Samson, writing for the Praxis upon the loss of the HMS Meurglys

The Hauteclaire class was a series of stopgap small vessels that used a boosted-chamber 16″ gun firing along the centerline. By opposing the recoil forces with the direct output of the gravity drive, it was made possible to fit a weapon of this size to such a small (some would say fragile) hull. These were to be used as pickets operating from a larger vessel or installation. While a hit from this weapon had a good chance of disabling all but the largest vessels, the reload rate made them only truly effective in packs. On their own, a miss with the initial shot left the vessel nearly motionless and defenseless but for her 5″ battery and smaller guns.

Depicted here is the loss of the HMS Meurglys to the German cruiser Gessler, the German operating in a commerce raiding role near one of the Mars trojans. The small asteroids and their associated debris served to shield vessels from being detected on the radioheliograph.

Another illustration for Spacecraft of the First World War.

The Bee-Zed asteroid orbits in the opposite direction to planets

In our solar system, an asteroid orbits the Sun in the opposite direction to the planets. Asteroid 2015 BZ509, also known as Bee-Zed, takes 12 years to make one complete orbit around the Sun. This is the same orbital period as that of Jupiter, which shares its orbit but moves in the opposite direction to the planet’s motion.

The asteroid with the retrograde co-orbit was identified by Helena Morais, a professor at São Paulo State University’s Institute of Geosciences & Exact Sciences (IGCE-UNESP). Morais had predicted the discovery two years earlier, so much so that the article describing observations of the asteroid published in Nature, is noted by Morais in the News & Views section of the same issue of the journal.

Keep reading

Two New Missions to Explore the Early Solar System

We’ve got big science news…!

We’ve just added two more science missions to our lineup! The two selected missions have the potential to open new windows on one of the earliest eras in the history of our solar system – a time less than 10 millions years after the birth of our sun.

The missions, known as Lucy and Psyche, were chosen from five finalists and will proceed to mission formulation.

Let’s take a dive into each mission…


Lucy, a robotic spacecraft, will visit a target-rich environment of Jupiter’s mysterious Trojan asteroids. Scheduled to launch in October 2021, the spacecraft is slated to arrive at its first destination, a main asteroid belt, in 2025. 

Then, from 2027 to 2033, Lucy will explore six Jupiter Trojan asteroids. These asteroids are trapped by Jupiter’s gravity in two swarms that share the planet’s orbit, one leading and one trailing Jupiter in its 12-year circuit around the sun. The Trojans are thought to be relics of a much earlier era in the history of the solar system, and may have formed far beyond Jupiter’s current orbit.

Studying these Trojan asteroids will give us valuable clues to deciphering the history of the early solar system.


The Psyche mission will explore one of the most intriguing targets in the main asteroid belt – a giant metal asteroid, known as 16 Psyche, about three times farther away from the sun than is the Earth. The asteroid measures about 130 miles in diameter and, unlike most other asteroids that are rocky or icy bodies, it is thought to be comprised of mostly metallic iron and nickel, similar to Earth’s core.

Scientists wonder whether psyche could be an exposed core of an early planet that could have been as large as Mars, but which lost its rocky outer layers due to a number of violent collisions billions of years ago.

The mission will help scientists understand how planets and other bodies separated into their layers early in their histories. The Psyche robotic mission is targeted to launch in October of 2023, arriving at the asteroid in 2030, following an Earth gravity assist spacecraft maneuver in 2024 and a Mars flyby in 2025.

Get even more information about these two new science missions HERE

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The 2 new upcoming NASA Discovery-Class missions (a category for lower cost missions) announced!  Lucy will visit the Trojan asteroids and Psyche will visit the asteroid Psyche, which appears to be almost entirely made of metal.


Ask Ethan: Does Earth Really Have A Second Moon?

“There are two different ways that a planet can have a natural satellite. The one you’re most familiar with – the path that the “old” Moon follows – occurs when an object is directly bound to its parent body. That means it has a certain speed and orbits at a certain distance from a planet to remain in direct orbit around it for an arbitrarily long time. It can’t be too far away or too elliptical in nature, or the tug from other worlds and objects in the Solar System will destroy or eject it over time. If we take a look at each one of the moons in the Solar System, they all have those characteristics.

But you don’t need to be directly bound to a planet in order to remain a natural satellite of it. Just as the planets are in stable orbits around the Sun, each orbital distance has its own stable or quasi-stable set of paths around it.”

Earlier this week, NASA announced the discovery of Asteroid 2016 HO3, calling it Earth’s second moon. And it turns out that this is an object in a stable orbit, the same distance from the Sun as the Earth, that can be found revolving around our world at a distance between 38 and 100 times the distance from us to the Moon. But that isn’t exactly the same as having a second Moon! In order to be considered not just a natural satellite but a stable one, you need to remain orbiting your parent world for a long period of time, not just tens, hundreds or thousands of years, like a transient quasi-satellite. Despite its current orbital characteristics, this object is much more akin to the multiple Trojan asteroids orbiting with our world than anything we’d consider moon-like.

Go get the full story on all of our so-called “second moons” on this week’s Ask Ethan!

What does it means to be a ‘planet’?

Before the discoveries of the early 21st century, astronomers had no real need for a formal definition for planets. With the discovery of Pluto in 1930, astronomers considered the Solar System to have nine planets, along with thousands of smaller bodies such as asteroids and comets. Pluto was thought to be larger than Mercury.

In 1978, the discovery of Pluto’s moon Charon radically changed this picture. By measuring Charon’s orbital period, astronomers could accurately calculate Pluto’s mass for the first time, which they found to be much smaller than expected. Pluto’s mass was roughly one twenty-fifth of Mercury’s, making it by far the smallest planet, smaller even than the Earth's Moon, although it was still over ten times as massive as the largest asteroid, Ceres.

In the 1990s, astronomers began finding other objects at least as far away as Pluto, now known as Kuiper Belt objects, or KBOs. Many of these shared some of Pluto’s key orbital characteristics and are now called plutinos. Pluto came to be seen as the largest member of a new class of objects, and some astronomers stopped referring to Pluto as a planet. Pluto’s eccentric and inclined orbit, while very unusual for a planet in the Solar System, fits in well with the other KBOs.

Starting in 2000, with the discovery of at least three bodies (Quaoar, Sedna, and Eris) all comparable to Pluto in terms of size and orbit, it became clear that either they all had to be called planets or Pluto would have to be reclassified. Astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. They were also concerned about the classification of planets in other planetary systems. In 2006, the matter came to a head with the measurement of the size of 2003 UB313. Eris (as it is now known) turned out to be slightly larger than Pluto, and so was thought to be equally deserving of the status of 'planet’.

The definition of planet set in Prague in 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which:

  1. is in orbit around the Sun,
  2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
  3. has “cleared the neighbourhood” around its orbit.

A non-satellite body fulfilling only the first two of these criteria is classified as a “dwarf planet”. According to the IAU, “planets and dwarf planets are two distinct classes of objects”. A non-satellite body fulfilling only the first criterion is termed a “small Solar System body” (SSSB). Initial drafts planned to include dwarf planets as a subcategory of planets, but because this could potentially have led to the addition of several dozens of planets into the Solar System, this draft was eventually dropped. The definition was a controversial one and has drawn both support and criticism from different astronomers, but has remained in use.

According to the definition, there are currently eight planets and five dwarf planets known in the Solar System. The definition distinguishes planets from smaller bodies and is not useful outside the Solar System, where smaller bodies cannot be found yet. Extrasolar planets, or exoplanets, are covered separately under a complementary 2003 draft guideline for the definition of planets, which distinguishes them from dwarf stars, which are larger.

There continues to be criticism regarding the wording of the final draft of the definition. Notably, the lead scientist on NASA’s robotic mission to PlutoAlan Stern, contends that, like Pluto, Earth, Mars, Jupiter and Neptune have not fully cleared their orbital zones either. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. “If Neptune had cleared its zone, Pluto wouldn’t be there”, he added.

Most astronomers counter this opinion by saying that, far from not having cleared their orbits, the major planets completely control the orbits of the other bodies within their orbital zone. Jupiter may coexist with a large number of small bodies in its orbit (the Trojan asteroids), but these bodies only exist in Jupiter’s orbit because they are in the sway of the planet’s huge gravity. Similarly, Pluto may cross the orbit of Neptune, but Neptune long ago locked Pluto and its attendant Kuiper belt objects, called plutinos, into a 3:2 resonance, i.e., they orbit the Sun twice for every three Neptune orbits. The orbits of these objects are entirely dictated by Neptune’s gravity, and thus, Neptune is gravitationally dominant.

The definition may be difficult to apply outside the Solar System. Techniques for identifying extrasolar objects generally cannot determine if an object has “cleared its orbit”, except indirectly via Stern and Levison’s Λ parameter, and provide limited information about when the objects were formed. The wording of the new definition is heliocentric in its use of the word Sun instead of star or stars, and is thus not applicable to the numerous objects that have been identified in orbit around other stars. However, a separate “working” definition for extrasolar planets was established by the IAU in 2001 and includes the criterion “the minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in the Solar System.”


13 Reasons to Have an Out of This World Friday (the 13th)

1. Know that not all of humanity is bound to the ground

Since 2000, the International Space Station has been continuously occupied by humans. There, crew members live and work while conducting important research that benefits life on Earth and will even help us eventually travel to deep space destinations, like Mars.

2. Smart people are up all night working in control rooms all over NASA to ensure that data keeps flowing from our satellites and spacecraft

Our satellites and spacecraft help scientists study Earth and space. Missions looking toward Earth provide information about clouds, oceans, land and ice. They also measure gases in the atmosphere, such as ozone and carbon dioxide, and the amount of energy that Earth absorbs and emits. And satellites monitor wildfires, volcanoes and their smoke.

Satellites and spacecraft that face toward space have a variety of jobs. Some watch for dangerous rays coming from the sun. Others explore asteroids and comets, the history of stars, and the origin of planets. Some fly near or orbit other planets. These spacecraft may look for evidence of water on Mars or capture close-up pictures of Saturn’s rings.

3. The spacecraft, rockets and systems developed to send astronauts to low-Earth orbit as part of our Commercial Crew Program is also helping us get to Mars

Changes to the human body during long-duration spaceflight are significant challenges to solve ahead of a mission to Mars and back. The space station allows us to perform long duration missions without leaving Earth’s orbit. 

Although they are orbiting Earth, space station astronauts spend months at a time in near-zero gravity, which allows scientists to study several physiological changes and test potential solutions. The more time they spend in space, the more helpful the station crew members can be to those on Earth assembling the plans to go to Mars.

4. Two new science missions will travel where no spacecraft has gone before…a Jupiter Trojan asteroid and a giant metal asteroid!

We’ve selected two missions that have the potential to open new windows on one of the earliest eras in the history of our solar system – a time less than 10 million years after the birth of our sun!

The first mission, Lucy, will visit six of Jupiter’s mysterious Trojan asteroids. The Trojans are thought to be relics of a much earlier era in the history of the solar system, and may have formed far beyond Jupiter’s current orbit.

The second mission, Psyche, will study a unique metal asteroid that’s never been visited before. This giant metal asteroid, known as 16 Psyche, is about three times farther away from the sun than is the Earth. Scientists wonder whether Psyche could be an exposed core of an early planet that could have been as large as Mars, but which lost its rocky outer layers due to a number of violent collisions billions of years ago.

5. Even astronauts eat their VEGGIES’s

NASA astronaut Shane Kimbrough collected the third and final harvest of the latest round of the Veggie investigation, testing the capability to grow fresh vegetables on the International Space Station. 

Understanding how plants respond to microgravity is an important step for future long-duration space missions, which will require crew members to grow their own food. Crew members have previously grown lettuce and flowers in the Veggie facility. This new series of the study expands on previous validation tests.

6. When you feel far away from home, you can think of the New Horizons spacecraft as it heads toward the Kuiper Belt, and the twin Voyager spacecraft are beyond the influence of our sun…billions of miles away 

Our New Horizons spacecraft completed its Pluto flyby in July 2015 and has continued on its way toward the Kuiper Belt. The spacecraft continues to send back important data as it travels toward deeper space at more than 32,000 miles per hour, and is nearly 3.2 billion miles from Earth.

In addition to New Horizons, our twin Voyager 1 and 2 spacecraft are exploring where nothing from Earth has flown before. Continuing on their more-than-37-year journey since their 1977 launches, they are each much farther away from Earth and the sun than Pluto. In August 2012, Voyager 1 made the historic entry into interstellar space, the region between the stars, filled with material ejected by the death of nearby stars millions of years ago.

7. Earth has a magnetic field that largely protects it from the solar wind stripping away out atmosphere…unlike Mars

Findings from our MAVEN mission have identified the process that appears to have played a key role in the transition of the Martian climate from an early, warm and wet environment to the cold, arid planet Mars is today. MAVEN data have enabled researchers to determine the rate at which the Martian atmosphere currently is losing gas to space via stripping by the solar wind. Luckily, Earth has a magnetic field that largely protects it from this process. 

8. There are humans brave enough to not only travel in space, but venture outside the space station to perform important repairs and updates during spacewalks

Spacewalks are important events where crew members repair, maintain and upgrade parts of the International Space Station. These activities can also be referred to as EVAs – Extravehicular Activities. Not only do spacewalks require an enormous amount of work to prepare for, but they are physically demanding on the astronauts. They are working in the vacuum of space in only their spacewalking suit. 

When on a spacewalk, astronauts use safety tethers to stay close to their spacecraft. One end of the tether is hooked to the spacewalker, while the other end is connected to the vehicle. Spacewalks typically last around 6.5 hours, but can be extended to 7 or 8 hours, if necessary.

9. We’re working to create new aircraft that will dramatically reduce fuel use, emissions and noise…meaning we could change the way you fly! 

The nation’s airlines could realize more than $250 billion dollars in savings in the near future thanks to green-related technologies that we are developing and refining. These new technologies could cut airline fuel use in half, pollution by 75% and noise to nearly one-eighth of today’s levels!

10. You can see a global image of your home planet…EVERY DAY

Once a day, we will post at least a dozen new color images of Earth acquired from 12 to 36 hours earlier. These images are taken by our EPIC camera from one million miles away on the Deep Space Climate Observatory (DSCOVR). Take a look HERE.

11. Employees of NASA have always been a mission driven bunch, who try to find answers that were previously unknown

The film “Hidden Figures,” focuses on the stories of Katherine Johnson, Mary Jackson and Dorothy Vaughan, African-American women who were essential to the success of early spaceflight. 

Today, we embrace their legacy and strive to include everyone who wants to participate in our ongoing exploration. In the 1960’s, we were on an ambitious journey to the moon, and the human computers portrayed in Hidden Figures helped get us there. Today, we are on an even more ambitious journey to Mars. We are building a vibrant, innovative workforce that reflects a vast diversity of discipline and thought, embracing and nurturing all the talent we have available, regardless of gender, race or other protected status. Take a look at our Modern Figures HERE.

12. A lot of NASA-developed tech has been transferred for use to the public 

Our Technology Transfer Program highlights technologies that were originally designed for our mission needs, but have since been introduced to the public market. HERE are a few spinoff technologies that you might not know about.

13. If all else fails, here’s an image of what we (Earth) and the moon look like from Mars  

From the most powerful telescope orbiting Mars comes a new view of Earth and its moon, showing continent-size detail on the planet and the relative size of the moon. The image combines two separate exposures taken on Nov. 20 by our High Resolution Imaging Science Experiment (HiRISE) camera on our Mars Reconnaissance Orbiter.

In the image, the reddish feature near the middle of the face of Earth is Australia.

Exciting NASA news

… as if there’s not been some of that already this week.

(Image credit: NASA/JPL)

It seems that NASA’s slated to select two proposals for their Discovery program missions.

A “Discovery” mission at NASA is generally a smaller mission that happens very quickly. Something like the Curiosity rover or the Cassini-Huygens mission aren’t Discovery program missions, those are called “Flagship” missions.

NASA’s incredible Dawn mission is a Discovery mission.

Right now the five missions under consideration are:

VERITAS (Venus Emissivity, Radio Science, InSAR Topography and Spectroscopy): Basically a mission that would orbit Venus (a planet deserving to be visited again) and map its surface with high resolution radar.

- Psyche: This mission would explore a huge, metal-rich asteroid in the asteroid belt. Important and potentially influential mission (there are lots of entrepreneurs looking for metal-rich asteroids to mine in the near future).

- Lucy: This mission would explore a series of “Trojan” asteroids, basically asteroids that trail behind Jupiter.

- NEOCam: This would search for dangerous near-Earth asteroids.

DAVINCI (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging): As you might guess from its name, this spacecraft would descend through the Venusian atmosphere, studying it as it goes down.

If the rumors I’ve heard are true, it’s possible NASA might be able to select two missions from this excellent pile.

What are your picks?

So yeah I kinda agree that Jim likes stars and shit but I would really like to see more of his love for science, because archeo astronomy is scientifically not that interesting. (ノ◕ヮ◕)ノ*:・゚✧

Give me theoretical astronomer Jim. ≖‿≖

Give me astrophysicus Jim. ( ´∀`)☆

Give me rants about trojan asteroid belts and rooms full with whiteboards with calculations on them that continue on the wallpaper because there was no more room and fuck you sebastian he’s not going to wipe out any of that shit. (✿ ♥‿♥)

I want to have him have stacks of notebooks full with solved astrophysical problems that would earn him millions while he’s deliberately waiting for the reward to get raised because he sure as hell is not give the solution to cosmic inflation or anything for a meager sum because he’s a little shit. (✿◠‿◠)

I want his fellow astronomers be terrified of him because have you heard what he has done to Stent better not go in the same field of research as Moriarty is because he might as well ruin your career when he feels like it. 。◕ ‿ ◕。

Sebastian all purring seductively “what’s on your mind baby” when Jim’s thinking and Jim’s answer being “is a non-spherically symmetric gravitational pull from outside the observable Universe responsible for some of the observed motion of large objects such as galactic clusters in the universe?” and Sebastian all  w h a t. (◕‿◕✿)

Just. Professor Jim. ʘ‿ʘ


give it to me

Solar System: Things to Know This Week

See our home planet from Mars, learn about our latest Discovery missions, see stunning imagery from the Cassini mission and more!

1. Our Home

The powerful HiRISE camera on the Mars Reconnaissance Orbiter took this incredible image of our home and moon. The image combines two separate exposures taken on Nov. 20, 2016. 

See more 

2. Our Latest Missions of Discovery

We’ve selected two new missions to explore the early solar system. Lucy, a robotic spacecraft scheduled to launch in October 2021, is slated to arrive at its first destination, a main belt asteroid, in 2025. From 2027 to 2033, Lucy will explore six Jupiter Trojan asteroids. These asteroids are trapped by Jupiter’s gravity in two swarms that share the planet’s orbit, one leading and one trailing Jupiter in its 12-year circuit around the sun.

+Learn more

Psyche, targeted to launch in October 2023, will explore one of the most intriguing targets in the main asteroid belt–a giant metal asteroid, known as 16 Psyche. The asteroid is about 130 miles (210 kilometers) in diameter and thought to be comprised mostly of iron and nickel, similar to Earth’s core.

+ Details

3. Image From Cassini  

Cassini took so many jaw-dropping photos last year, how could anyone choose just 10? Well, the Cassini team didn’t. Here are 17 amazing photos from Saturn and its moons last year.

4. The Colors of Mars

Impact craters have exposed the subsurface materials on the steep slopes of Mars. However, these slopes often experience rockfalls and debris avalanches that keep the surface clean of dust, revealing a variety of hues, like in this enhanced-color image from our Mars Reconnaissance Orbiter, representing different rock types. 

+ Learn more

5. More From New Horizons

Even though our New Horizons mission flew by Pluto in 2015, the scientific discoveries keep coming. Using a model similar to what meteorologists use to forecast weather and a computer simulation of the physics of evaporating ices, scientists have found evidence of snow and ice features that, until now, had only been seen on Earth.

Discover the full list of 10 things to know about our solar system this week HERE.

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