Setting foot on a distant planet… we’ve all dreamed about it at one time or another. And it has been a staple of science fiction for almost a century. Engage the warp dive, spool up the FLT, open a wormhole, or jump into the cryochamber. Next stop, Alpha Centauri (or some other star)! But when it comes to turning science fiction into science fact, there are certain unfortunate realities we have to contend with. For starters, none of the technology for faster-than-light travel exists!
Second, sending crewed mission to even the nearest planets is a very expensive and time consuming endeavor. But thanks to ongoing developments in the fields of miniaturization, electronics and direct-energy, it might be possible to send tiny spacecraft to distant stars in a single lifetime, which could carry something of humanity along with them. Such is the hope of Professor Philip Lubin and Travis Bradshears, the founders of “Voices of Humanity“.
For people familiar with directed-energy concepts, the name Philip Lubin should definitely ring a bell. A professor from the University of California, Santa Barbara (UCSB), he is also the mind behind the NASA-funded Directed Energy Propulsion for Interstellar Exploraiton (DEEP-IN) project, and the Directed Energy Interstellar Study. These projects seek to use laser arrays and large sails to achieve relativistic flight for the sake of making interstellar missions a reality.
Looking beyond propulsion and into the realm of public participation in space exploration, Prof. Lubin and Bradshears (an engineering and physics student from the University of California, Berkeley) came together to launch Voices of Humanity (VoH) in 2015. Inspired by their work with NASA, this Kickstarter campaign aims to create the world’s first “Space Time Capsule”.
Intrinsic to this is the creation of a Humanity Chip, a custom semiconductor memory device that can be attached to the small, wafer-scale spacecraft that are part of DEEP-IN and other directed-energy concepts. This chip will contain volumes of data, including tweets, media files, and even the digital DNA records of all those who want to take part in the mission. As Professor Lubin told Universe Today in a phone interview:
“We wanted to put on board some part of humanity. We couldn’t shrink ray people down, so Travis and I brainstormed and thought that the next best thing would be to allow people to become digital astronauts. We wanted to pave the way for interstellar missions where we could send the essence of humanity to the stars – “Emissaries of the Earth”, if you will. We wanted to pave the way for that.”
This digital archive would be similar to the Golden Record that was placed on the Voyager probes, but would be much more sophisticated. Taking advantage of all the advances made in computing, electronics and data storage in recent decades, it would contain many millions of times the data, but comprise a tiny fraction of the volume.
In fact, as Lupin explained, the state of technology today allows us to create a digital archive that would be about the same size a fingernail, and which would require no more than a single gram of mass to be allocated on a silicon wafer-ship. And while such a device is not the same as sending astronauts on interstellar voyages to explore other planets, it does allow humanity to send something of itself.
“We now have the technology to put a message from everyone on Earth onto a small piece of a tiny spacecraft,” said Lupin. “We want to begin today, and not just for the future, by putting information onto anything that is launched from Earth. We are the point technologically, at this moment, that we could put a small portion of humanity on this spacecraft.”
In essence, human beings would be able to create the interstellar equivalent of a “Baby on Board” sticker, except for humanity instead. This sticker would be no larger than a postage stamp, and could be mounted on every craft to leave Earth in the near future. In essence, all missions departing from Earth could have “Humanity on Board”.
The plan is to launch their first chip – Humanity Chip 1.0 – into Low Earth Orbit (LEO) in 2017. This will be followed by the creation of Humanity Chip 2.0, which take advantage of the developments that will have occurred by next year. Eventually, they hope that Humanity Chips will be a part of missions that increase in distance from Earth, eventually culminating in a mission to interstellar space.
Artist’s rendition of The Humanity chip placed on a silicon wafer spacecraft. Credit: Voices of Humanity/kickstarter.com
While there are no deep-space missions ready to go just yet, several concepts are on the table for interplanetary missions that will rely on wafer-scale spacecraft (like NASA’s DEEP-IN concept). If their Kickstarter campaign succeeds in raising the $30,000 necessary to create a Humanity Chip, Prof. Lubin and Bradshears also hope to create a “Black Hole Chip”, where participants will be able to record their “less than happy” thoughts as part of the data, which will then be sent off into space forever.
They also have a stretch goal in mind, known as the “Beam Me Up” objective. In the event that their campaign is able to raise $100,000, they will use the funds to create a ground-based laser array that will beam a package of encoded data towards a target destination in space.
As of the penning of this article, Prof. Lubin and Bradshears have raised a total of $5,656 towards their goal of $30,000. The campaign kicked off earlier this month and will remain open for another 22 days. So if you’re interested in contributing to Humanity Chip 1.0, or becoming an “Emissary of the Earth”, there’s still plenty of time.
In addition to his work with NASA, Prof. Lubin is also responsible for the UCSB’s Directed Energy System for Targeting of Asteroids and ExploRation (DE-STAR) project, a proposed system that would use directed energy (i.e. big lasers!) to deflect asteroids, comets, and other near-Earth objects (NEOs) that could pose a risk to planet Earth.
The Black Hole Chip is one of the stretch goals, which will send “less than happy” thoughts into space. Credit: Voices of Humanity/kickstarter.com
And, in a recent article titled “The Search for Directed Intelligence“- which appeared in the March 2016 issue of REACH – Reviews in Human Space Exploration – Lupin indicated that advances in directed-energy applications might also help in the search for extra-terrestrial intelligence. Essentially, by looking for for sources of directed energy systems, he claims, we might be able to find our way to other civilizations.
It is an exciting age, where advances in telecommunications and electronics are allowing us to overcome the vast distances involved in space travel. In the future, astronauts may rely on robotic explorers and fast-as-light communications to explore distant worlds (a process known as telexploration). And with a digital archive on board, we will be able to send personal greetings to any life that may already exist there.
For those who would say “sharing personal information with extra-terrestrials is a bad idea”, I would remind them that they (probably) don’t have access to Twitter or our financial records. All the same, it might be wise not to include your Social Security (or Social Insurance) number in the recordings, or any other personal data you wouldn’t share with strangers!
And who knows? Someday, we may start colonizing other planets by sending our DNA there direct. The truth is always stranger than fiction, after all!
And be sure to check out this video produced by Voices for Humanity:
Totality! The view of the last total solar eclipse to cross a U.S. state (Hawaii) back in 1991. Image credit and copyright: A. Nartist (shot from Cabo San Lucas, Baja California).
One. More. Year. Quick; where will you be this time next year on August 21st, 2017? We’re now just one year out this weekend from a fine total solar eclipse gracing the United States from coast to coast. If you think one year out is too early to start planning, well, umbraphiles (those who chase the shadow of the Moon worldwide) have been planning to catch this one now for over a decade.
The shadow of the March 9th, 2016 solar eclipse (the dark spot on the right) as seen from the Himawari-8 Earth-observing satellite. Image credit: JAXA/JMA/Himawari/CIMSS.
Get set for the Great American Eclipse. The last time a total solar eclipse made landfall over a U.S. state was Hawaii on July 11th, 1991, and the path of totality hasn’t touched down over the contiguous ‘Lower 48’ United States since February 26th, 1979. And you have to go all the way back over nearly a century to June 8th, 1918 to find an eclipse that exclusively crossed the United States from the Pacific to the Atlantic Coast.
The path of the 2017 total solar eclipse across the U.S. Image credit and copyright: Michael Zeiler/The GreatAmercianEclipse
Totality for the August 21st, 2017 eclipse crosses over many major cities, including Columbia South Carolina, Nashville, St. Louis and Salem, Oregon. The inner shadow of the Moon touches on 15 states as it races across the U.S. in just over an hour and a half. The length of totality is about 2 minutes in duration as the shadow makes landfall near Lincoln City, Oregon, reaches a maximum duration of 2 minutes, 42 seconds very near Carbondale, Illinois, and shrinks back down to 2 minutes and 35 seconds as the shadow heads back out to sea over Charleston, South Carolina.
The eclipse will be a late morning affair in the northwest, occurring at high noon over western Nebraska, and early afternoon to the east. ‘Getting your ass to totality,’ is a must. “But I’ve seen a partial solar eclipse,” is a common refrain, “aren’t they all the same?”
An animation of the 2017 eclipse.
Nope. We witnessed the May 10th, 1994 annular eclipse from the shores of Lake Erie, and can tell you that even less than 1% of the Sun’s intensity is still pretty bright, a steely blue luminosity equivalent to a cloudy day.
We crisscrossed the United States along the eclipse path back in 2014, chronicling preparations in towns such as Columbia and Hopkinsville, Kentucky. Last minute accommodation is already tough to come by, even one year out. Cabins in the Land Between the Lakes region near Paducah, Kentucky, for example, were booked full as soon as the August 21st date became available. Think Mardi Gras and DragonCon, rolled into one. Hopkinsville also has an annual Roswell-style UFO-fest on the same date, celebrating the 1955 Kelly-Hopkinsville UFO incident.
Will it be ‘umbraphiles versus aliens?’
Out west, enticing locales include the Grand Teton National Park and Jackson Hole, Wyoming and the northern edge of the Craters of the Moon National Monument site in Idaho. It’s also worth noting that the western United States is a better bet cloud cover-wise, as afternoon summer thundershowers tend to be the norm for the southeast during late August.
Millions live within an easy day drive of the eclipse path, and it happens during prime camping season, to boot. The annual Sturgess motorcycle rally held near Rapid City, South Dakota is just one week prior to totality, and bikers returning from the pilgrimage southward could easily stop to greet the Earth’s shadow on the road home.
There’s been talk that Cosmoquest may mount an eclipse expedition based out of Nashville, Tennessee (more to come on that).
Maintaining mobility is the best bet. Our master plan is to return to the States a week or so prior, rent a camper van from Vegas, and head northward. Like millions of Americans, this will be our first total solar eclipse, and the event promises to spark a whole new generation of umbraphiles. And stick around just seven more years, and totality will again cross the United States on August 8th, 2024 from the southwest to the northeast. The Illinois, Missouri and Kentucky tri-state region sees this eclipse as well. This one is special for us, as it crosses over our hometown of Presque Isle, Maine. I remember looking up the next total solar eclipse over northern Maine as a kid, way back when, and figuring out just how old I would be. The top of Mount Katahdin and selected sites along the Maine Solar System model would all be choice locales to view this one. Check out this great old vid of the aforementioned 1979 eclipse over the U.S.:
We also plan on taking the veteran eclipse-chaser’s mantra of ‘experience your first eclipse; but photograph your second one.’ to heart. Lots of fascinating projects are afoot leading up to the 2017 total solar eclipse, including The Eclipse MegaMovie Project to produce a complete video documentary of the eclipse path, plans by a student group to fly and observe the eclipse from balloons during totality, proposals to replicate famous eclipse experiments and more. It’s also worth noting that the bright star Regulus will sit just one degree from the Sun during totality… perhaps someone will manage to measure its deflection via General Relativity in a manner similar to Sir Arthur Eddington’s famous 1919 observation?
Unlike the paths of most eclipses, which seem to have an affinity for wind-swept tundra or remote swaths of desert, this one is sure to draw in the ‘astronomy-curious’ and may just be the most witnessed total solar eclipse in history.
Here’s some eclipse tales and facts to ponder leading up to totality. If you caught the August 11th, 1999 eclipse across Europe, then you saw the last eclipse in the same saros series 145. If you caught the eclipse before that in the same series on July 31st, 1981 across northeast Asia, then you’ll complete a 54 year long triple-saros period after seeing next summer’s eclipse, known as an exeligmos. This cycle also brings the eclipse path very nearly back around to the same longitude.
Regulus near the eclipsed Sun next August. Credit: Stellarium.
The Sun is about 400 times larger than the Moon in diameter, but the Moon is 400 times closer. We’ve actually heard this fact tossed out as evidence for intelligent design, though it’s just a happy celestial circumstance of our present era. In fact, annular eclipses are now slightly more common than totals in our current epoch, and will continue to become more so as the Moon slowly recedes from the Earth. Just under a billion years ago, the very first annular eclipse of the Sun as seen from the Earth occurred, and 1.4 billion years hence, the Earth will witness one last brief total eclipse.
But you won’t have to wait that long. Don’t miss the greatest show in the universe next August!
Artist’s impression of a sunset seen from the surface of an Earth-like exoplanet. Credit: ESO/L. Calçada
The hunt for exoplanets has been heating up in recent years. Since it began its mission in 2009, over four thousand exoplanet candidates have been discovered by the Kepler mission, several hundred of which have been confirmed to be “Earth-like” (i.e. terrestrial). And of these, some 216 planets have been shown to be both terrestrial and located within their parent star’s habitable zone (aka. “Goldilocks zone”).
But in what may prove to be the most exciting find to date, the German weekly Der Spiegel announced recently that astronomers have discovered an Earth-like planet orbiting Proxima Centauri, just 4.25 light-years away. Yes, in what is an apparent trifecta, this newly-discovered exoplanet is Earth-like, orbits within its sun’s habitable zone, and is within our reach. But is this too good to be true?
For over a century, astronomers have known about Proxima Centauri and believed that it is likely to be part of a trinary star system (along with Alpha Centauri A and B). Located just 0.237 ± 0.011 light years from the binary pair, this low-mass red dwarf star is also 0.12 light years (~7590 AUs) closer to Earth, making it the closest star system to our own.
In the past, the Kepler mission has revealed several Earth-like exoplanets that were deemed to be likely habitable. And recently, an international team of researchers narrowed the number of potentially-habitable exoplanets in the Kepler catalog down to the 20 that are most likely to support life. However, in just about all cases, these planets are hundreds (if not thousands) of light years away from Earth.
Knowing that there is a habitable planet that a mission from Earth could reach within our own lifetimes is nothing short of amazing! But of course, there is reason to be cautiously optimistic. Citing anonymous sources, the magazine stated:
“The still nameless planet is believed to be Earth-like and orbits at a distance to Proxima Centauri that could allow it to have liquid water on its surface — an important requirement for the emergence of life. Never before have scientists discovered a second Earth that is so close by.”
In addition, they claim that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory‘s reflecting telescope. Coincidentally, it was this same observatory that announced the discovery of Alpha Centauri Bb back in 2012, which was also declared to be “the closest exoplanet to Earth”. Unfortunately, subsequent analysis cast doubt on its existence, claiming it was a spurious artifact of the data analysis.
Artist’s impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B by the European Southern Observatory on October 17, 2012. Credit: ESO
However, according to Der Spiegel’s unnamed source – whom they claim was involved with the La Silla team that made the find – this latest discovery is the real deal, and was the result of intensive work. “Finding small celestial bodies is a lot of hard work,” the source was quoted as saying. “We were moving at the technically feasible limit of measurement.”
The article goes on to state that the European Southern Observatory (ESO) will be announcing the finding at the end of August. But according to numerous sources, in response to a request for comment by AFP, ESO spokesman Richard Hook refused to confirm or deny the discovery of an exoplanet around Proxima Centauri. “We are not making any comment,” he is reported as saying.
What’s more, the folks at Project Starshot are certainly excited by the news. As part of Breakthrough Initiatives – a program founded by Russian billionaire Yuri Milner to search for intelligent life (with backing from Stephen Hawking and Mark Zuckerberg) – Starshot intends to send a laser-sail driven-nanocraft to Alpha Centauri in the coming years.
This craft, they claim, will be able to reach speeds of up to 20% the speed of light. At this speed, it will able to traverse the 4.37 light years that lie between Earth and Alpha Centauri in just 20 years. But with the possible discovery of an Earth-like planet orbiting Proxima Centauri, which lies even closer, they may want to rethink that objective.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
As Professor Phillip Lubin – a professor at the University of California, Santa Barbara, the brains behind Project Starshot, and a key advisor to NASA’s DEEP-IN program – told Universe Today via email:
“The discovery of possible planet around Proxima Centauri is very exciting. It makes the case of visiting nearby stellar systems even more compelling, though we know there are many exoplanets around other nearby stars and it is very likely that the Alpha Centauri system will also have planets.”
Naturally, there is the desire (especially amongst exoplanet enthusiasts) to interpret the ESO’s refusal to comment either way as a sort of tacit confirmation. And knowing that industry professionals are excited it about it does lend an air of legitimacy. But of course, assuming anything at this point would be premature.
If the statements made by the unnamed source, and quoted by Der Speigel, are to be taken at face value, then confirmation (or denial) will be coming shortly. In the meantime, we’ll all just need to be patient. Still, you have to admit, it’s an exciting prospect: an Earth-like planet that’s actually within reach! And with a mission that could make it there within our own lifetimes. This is the stuff good science fiction is made of, you know.
A brilliant Perseid meteor streaks along the Summer Milky Way as seen from Cinder Hills Overlook at Sunset Crater National Monumen at 2:40 a.m. (9:40 UT) August 12. It left a glowing ion trail that lasted about 30 seconds. The camera caught a twisting smoke trail that drifted southward over the course of several minutes. Credit: Jeremy Perez
The Perseid meteor shower must have looked fantastic from 10,000 feet. That’s how high you would have had to go to get past the pervasive fog and overcast skies at my home last night. Tonight looks a little better for weather, so I’ll do what all hopeful amateurs astronomers do. Set the alarm for 2 a.m. and peek out the shade looking for those glimmers of starlight that indicate clear skies.
A composite photo, made from images taken last night August 11-12 from the UK, captures multiple Perseids. Credit: Peter Greig
From observations reported as of mid-afternoon to the International Meteor Observers 2016 Perseids Quick-Look site, it appears the greatest activity or highest meteor counts happened over Europe and points east in two outbursts: a brief but intense display around 23:15 Universal Time (6:15 p.m. CDT in daylight) August 11 when some observers briefly saw up to 15 Perseids a minute (!) with many bright ones, and a second peak starting around 2:00 UT (9 p.m. CDT) and lasting till 5:00 UT (midnight CDT).
90+ Perseid meteors captured on video August 11-12, 2016 by Ohio amateur John Chumack
While Europeans clearly hit the jackpot — some observers calling it the best since the 2002 Leonid storm — U.S. observers varied in their meteor counts. A few thought the shower was a bust, others reported numbers more typical of an “average year” shower. It appears that Earth passed through a dense filament of comet dust while it was night in Europe but late afternoon in the Americas. C’est la vie météore!
We should be past peak by today, but experience shows that tonight should still be a very good time for Perseid watching. Indeed, the next few nights will reward skywatchers with at least a dozen an hour. I’ll be out watching and hopefully not imagining what’s happening 10,000 feet over my head. Good luck to you too!
The moons of solar system, showed to scale with Earth's Moon. Credit: NASA
For millennia, human beings stared up at the night sky and were held in awe by the Moon. To many ancient cultures, it represented a deity, and its cycles were accorded divine significance. By the time of Classical Antiquity and the Middle Ages, the Moon was considered to be a heavenly body that orbited Earth, much like the other known planets of the day (Mercury, Venus, Mars, Jupiter, and Saturn).
However, our understanding of moons was revolutionized when in 1610, astronomer Galileo Galilei pointed his telescope to Jupiter and noticed ” four wandering stars” around Jupiter. From this point onward, astronomers have come to understand that planets other than Earth can have their own moons – in some cases, several dozen or more. So just how many moons are there in the Solar System?
In truth, answering that question requires a bit of clarification first. If we are talking about confirmed moons that orbit any of the planets of the Solar System (i.e. those that are consistent with the definition adopted by the IAU in 2006), then we can say that there are currently 207 known moons. If however, we open the floor to “dwarf planets” that have confirmed satellites, the number reached 220.
The moons, several minor planets, and comets of the Solar System shown to scale. Credit: Antonio Ciccolella
However, 479 minor-planet moons have also been observed in the Solar System (as of Dec. 2022). This includes the 229 known objects in the asteroid belt with satellites, six Jupiter Trojans, 91 near-Earth objects (two with two satellites each), 31 Mars-crossers, and 84 natural satellites of Trans-Neptunian Objects. And some 150 additional small bodies have been observed within the rings of Saturn. If we include all these, then we can say that the Solar System has 849 known satellites.
Inner Solar System:
The planets of the Inner Solar system – Mercury, Venus, Earth, and Mars – are all terrestrial planets, which means that they are composed of silicate rock and minerals that are differentiated between a metallic core and a silicate mantle and crust. For a number of reasons, few satellites exist within this region of the Solar System.
All told, only three natural satellites exist orbiting planetary bodies in the Inner Solar System – Earth and Mars. While scientists theorize that there were moons around Mercury and Venus in the past, it is believed that these moons impacted the surface a long time ago. The reason for this sparseness of satellites has a lot to do with the gravitational influence of the Sun.
Both Mercury and Venus are too close to the Sun to have grabbed onto a passing object or held onto rings of debris in orbit that could have coalesced to form a satellite over time. In Mercury’s case, it is also too weak in terms of its own gravitational pull to grab a satellite in its orbit. Earth and Mars were able to retain satellites, but mainly because they are the outermost of the Inner planets.
Earth has only one natural satellite, which we are familiar with – the Moon. With a mean radius of 1737 km (1,080 mi) and a mass of 7.3477 x 10²² kg, the Moon is 0.273 times the size of Earth and 0.0123 as massive, which is quite large for a satellite. It is also the second densest moon in our Solar System (after Io), with a mean density of 3.3464 g/cm³.
Several theories have been proposed for the formation of the Moon. The prevailing hypothesis today is that the Earth-Moon system formed as a result of an impact between the newly-formed proto-Earth and a Mars-sized object (named Theia) roughly 4.5 billion years ago. This impact would have blasted material from both objects into orbit, where it eventually accreted to form the Moon.
Mars, meanwhile, has two moons – Phobos and Deimos. Like our own Moon, both of the Martian moons are tidally locked to Mars, so they always present the same face to the planet. Compared to our Moon, they are rough and asteroid-like in appearance and also much smaller. Hence the prevailing theory is that they were once asteroids that were kicked out of the Main Belt by Jupiter’s gravity and were then acquired by Mars.
The larger moon is Phobos, whose name comes from the Greek word which means “fear” (i.e. phobia). Phobos measures just 22.7 km (14 mi) across and has an orbit that places it closer to Mars than Deimos. Compared to Earth’s own Moon — which orbits at a distance of 384,403 km (238,857 mi) away from our planet — Phobos orbits at an average distance of only 9,377 km (5,826.5 mi) above Mars.
Phobos and Deimos, photographed here by the Mars Reconnaissance Orbiter. Credit: NASA
Mars’ second moon is Deimos, which takes its name from the Greek word for panic. It is even smaller, measuring just 12.6 km (7.83 mi) across, and is also less irregular in shape. Its orbit places it much farther away from Mars, at a distance of 23,460 km (14,577 mi), which means that Deimos takes 30.35 hours to complete an orbit around Mars.
These three moons are the sum total of moons to be found within the Inner Solar System (at least, by the conventional definition). But looking further abroad, we see that this is really just the tip of the iceberg. To think we once believed that the Moon was the only one of its kind!
Outer Solar System:
Beyond the Asteroid Belt (and Frost Line), things become quite different. In this region of the Solar System, every planet has a substantial system of Moons; in the case of Jupiter and Saturn, reaching perhaps even into the hundreds. So far, a total of 213 moons have been confirmed orbiting the Outer Planets, while several hundred more orbit minor bodies and asteroids.
Due to its immense size, mass, and gravitational pull, Jupiter has the most satellites of any planet in the Solar System. At present, the Jovian system includes 80 known moons, though it is estimated that it may have over 200 moons and moonlets (the majority of which are yet to be confirmed and classified).
The four largest Jovian moons are known as the Galilean Moons (named after their discoverer, Galileo Galilei). They include Io, the most volcanically active body in our Solar System; Europa, which is suspected of having a massive subsurface ocean; Ganymede, the largest moon in our Solar System; and Callisto, which is also thought to have a subsurface ocean and features some of the oldest surface material in the Solar System.
Illustration of Jupiter and the Galilean satellites. Credit: NASA
Then there’s the Inner Group (or Amalthea group), which is made up of four small moons that have diameters of less than 200 km (124 mi), orbit at radii less than 200,000 km (124,275 mi), and have orbital inclinations of less than half a degree. This group includes the moons of Metis, Adrastea, Amalthea, and Thebe. Along with a number of as-yet-unseen inner moonlets, these moons replenish and maintain Jupiter’s faint ring system.
Jupiter also has an array of Irregular Satellites, which are substantially smaller and have more distant and eccentric orbits than the others. These moons are broken down into families that have similarities in orbit and composition and are believed to be largely the result of collisions from large objects that were captured by Jupiter’s gravity.
Similar to Jupiter, it is estimated that Saturn has at least 150 moons and moonlets, but only 83 of these moons have been given official names or designations. Of these, 57 are less than 10 km (6.2 mi) in diameter, and another 13 are between 10 and 50 km (6.2 to 31 mi) in diameter. However, some of its inner and outer moons are rather large, ranging from 250 to over 5000 km (155 to 3100 mi)
Traditionally, most of Saturn’s moons have been named after the Titans of Greek mythology and are grouped based on their size, orbits, and proximity to Saturn. The innermost moons and regular moons all have small orbital inclinations and eccentricities and prograde orbits. Meanwhile, the irregular moons in the outermost regions have orbital radii of millions of kilometers, orbital periods lasting several years, and move in retrograde orbits.
A collage of Saturn (bottom left) and some of its moons: Titan, Enceladus, Dione, Rhea and Helene. Credit: NASA/JPL/Space Science Institute
The Inner Large Moons, which orbit within the E Ring, include the larger satellites MimasEnceladus, Tethys, and Dione. These moons are all composed primarily of water ice and are believed to be differentiated into a rocky core and an icy mantle and crust. The Large Outer Moons, which orbit outside of Saturn’s E Ring, are similar in composition to the Inner Moons – i.e. composed primarily of water ice, and rock.
At 5,150 km (3,200 mi) in diameter and 1,350×1020 kg in mass, Titan is Saturn’s largest moon and comprises more than 96% of the mass in orbit around the planet. Titan is also the only large moon to have its own atmosphere, which is cold, dense, and composed primarily of nitrogen with a small fraction of methane. Scientists have also noted the presence of polycyclic aromatic hydrocarbons in the upper atmosphere, as well as methane ice crystals.
The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters, evidence of cryo-volcanoes, and longitudinal dune fields that were apparently shaped by tidal winds. Titan is also the only body in the Solar System aside from Earth to have bodies of liquid on its surface. These take the form of methane–ethane lakes in Titan’s north and south polar regions.
Uranus has 27 known satellites, which are divided into the categories of larger moons, inner moons, and irregular moons (similar to other gas giants). The largest moons of Uranus are, in order of size, Miranda, Ariel, Umbriel, Oberon, and Titania. These moons range in diameter and mass from 472 km (293 mi) and 6.7×1019 kg for Miranda to 1578 km (980.5 mi) and 3.5×1021 kg for Titania. Each of these moons is particularly dark, with low bond and geometric albedos. Ariel is the brightest, while Umbriel is the darkest.
A montage of Uranus’s moons (from left to right) – Ariel, Credit: NASA
All of the large moons of Uranus are believed to have formed in the accretion disc, which existed around Uranus for some time after its formation or resulted from the large impact suffered by Uranus early in its history. Each one is comprised of roughly equal amounts of rock and ice, except for Miranda, which is made primarily of ice.
The ice component may include ammonia and carbon dioxide, while the rocky material is believed to be composed of carbonaceous material, including organic compounds (similar to asteroids and comets). Their compositions are believed to be differentiated, with an icy mantle surrounding a rocky core.
Neptune has 14 known satellites, all but one of which are named after Greek and Roman deities of the sea (except for S/2004 N 1, which is currently unnamed). These moons are divided into two groups – the regular and irregular moons – based on their orbit and proximity to Neptune. Neptune’s Regular Moons – Naiad, Thalassa, Despina, Galatea, Larissa, S/2004 N 1, and Proteus – are those that are closest to the planet and which follow circular, prograde orbits that lie in the planet’s equatorial plane.
Neptune’s irregular moons consist of the planet’s remaining satellites (including Triton). They generally follow inclined eccentric and often retrograde orbits far from Neptune. The only exception is Triton, which orbits close to the planet, following a circular orbit, though retrograde and inclined.
Global Color Mosaic of Triton, taken by Voyager 2 in 1989. Credit: NASA/JPL/USGS
In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Neso, and Psamathe – a group that includes both prograde and retrograde objects. With the exception of Triton and Nereid, Neptune’s irregular moons are similar to those of other giant planets and are believed to have been gravitationally captured by Neptune.
With a mean diameter of around 2,700 km (1,678 mi) and a mass of 21,4080 ± 520×1017 kg, Triton is the largest of Neptune’s moons and the only one large enough to achieve hydrostatic equilibrium (i.e. is spherical in shape). At a distance of 354,759 km (220,437 mi) from Neptune, it also sits between the planet’s inner and outer moons.
These moons make up the lion’s share of natural satellites found in the Solar System. However, thanks to ongoing exploration and improvements made in our instrumentation, satellites are being discovered in orbit around minor bodies as well.
Dwarf Planets and Other Bodies:
As already noted, there are several dwarf planets, TNOs, and other bodies in the Solar System that also have their own moons. These consist mainly of the natural satellites that have been confirmed orbiting Pluto, Eris, Haumea, and Makemake. With five orbiting satellites, Pluto has the most confirmed moons (though that may change with further observation).
The largest and closest in orbit to Pluto is Charon. This moon was first identified in 1978 by astronomer James Christy using photographic plates from the United States Naval Observatory (USNO) in Washington, D.C. Beyond Charon lies the four other circumbinary moons – Styx, Nix, Kerberos, and Hydra, respectively.
A portrait from the final approach of the New Horizons spacecraft to the Pluto system on July 11th, 2015. Credit: NASA-JHUAPL-SWRI.
Nix and Hydra were discovered simultaneously in 2005 by the Pluto Companion Search Team using the Hubble Space Telescope. The same team discovered Kerberos in 2011. The fifth and final satellite, Styx, was discovered by the New Horizons spacecraft in 2012 while capturing images of Pluto and Charon.
Charon, Styx, and Kerberos are all massive enough to have collapsed into a spheroid shape under their own gravity. Nix and Hydra, meanwhile, are oblong in shape. The Pluto-Charon system is unusual since it is one of the few systems in the Solar System whose barycenter lies above the primary’s surface. In short, Pluto and Charon orbit each other, causing some scientists to claim that it is a “double-dwarf system” instead of a dwarf planet and an orbiting moon.
In addition, it is unusual in that each body is tidally locked to the other. Charon and Pluto always present the same face to each other, and from any position on either body, the other is always at the same position in the sky or always obscured. This also means that the rotation period of each is equal to the time it takes the entire system to rotate around its common center of gravity.
In 2007, observations by the Gemini Observatory of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers. This would seem to indicate that Pluto has a warm subsurface ocean and that the core is geologically active. Pluto’s moons are believed to have been formed by a collision between Pluto and a similar-sized body early in the history of the Solar System. The collision released material that consolidated into the moons around Pluto.
Comparison of Pluto with the other largest TNOs and with Earth (all to scale). Credit: NASA/Lexicon
Coming in second is Haumea, which has two known moons – Hi’iaka and Namaka – which are named after the daughters of the Hawaiian goddess. Both were discovered in 2005 by Brown’s team while conducting observations of Haumea at the W.M. Keck Observatory. Hi’iaka, which was initially nicknamed “Rudolph” by the Caltech team, was discovered on January 26th, 2005.
It is the outer, the larger (at roughly 310 km (mi) in diameter), and brighter of the two, and orbits Haumea in a nearly circular path every 49 days. Infrared observations indicate that its surface is almost entirely covered by pure crystalline water ice. Because of this, Brown and his team have speculated that the moon is a fragment of Haumea that broke off during a collision.
Namaka, the smaller and innermost of the two, was discovered on June 30th, 2005, and nicknamed “Blitzen”. It is a tenth the mass of Hi‘iaka and orbits Haumea in 18 days in a highly elliptical orbit. Both moons circle Haumea is highly eccentric orbits. No estimates have been made yet as to their mass.
Eris has one moon called Dysnomia, named after the daughter of Eris in Greek mythology, and was first observed on September 10th, 2005 – a few months after the discovery of Eris. The moon was spotted by a team using the Keck telescopes in Hawaii, who were busy carrying out observations of the four brightest TNOs (Pluto, Makemake, Haumea, and Eris) at the time.
Artist’s concept of the dwarf planet Eris and its only natural satellite, Dysnomia. Credit: NASA, ESA, Adolph Schaller (for STScI)
In April 2016, observations using the Hubble Space Telescope‘s Wide Field Camera 3 revealed that Makemake had a natural satellite – which was designated S/2015 (136472) 1 (nicknamed MK 2 by the discovery team). It is estimated to be 175 km (110 mi) km in diameter and has a semi-major axis at least 21,000 km (13,000 mi) from Makemake.
Largest and Smallest Moons:
The title of “largest moon in the Solar System” goes to Ganymede, which measures 5,262.4 kilometers (3,270 mi) in diameter. This not only makes it larger than Earth’s Moon but larger even than the planet Mercury – though it has only half of Mercury’s mass. As for the smallest satellite, that is a tie between S/2003 J 9 and S/2003 J 12. These two satellites, both of which orbit Jupiter, measure about 1 km (0.6 mi) in diameter.
An important thing to note when discussing the number of known moons in the Solar System is that the key word here is “known”. With every passing year, more satellites are being confirmed, and the vast majority of those we now know about were only discovered in the past few decades. As our exploration efforts continue and our instruments improve, we may find that there are hundreds more lurking around out there!
Between the orbits of Mars and Jupiter lies the Solar System’s Main Asteroid Belt. Consisting of millions of objects that range in size from hundreds of kilometers in diameter (like Ceres and Vesta) to one kilometer or more, the Asteroid Belt has long been a source of fascination for astronomers. Initially, they wondered why the many objects that make it up did not come together to form a planet. But more recently, human beings have been eyeing the Asteroid Belt for other purposes.
Whereas most of our efforts are focused on research – in the hopes of shedding additional light on the history of the Solar System – others are looking to tap for its considerable wealth. With enough resources to last us indefinitely, there are many who want to begin mining it as soon as possible. Because of this, knowing exactly how long it would take for spaceships to get there and back is becoming a priority.
Distance from Earth:
The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the edge of the Belt that is closest to it can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi).
The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons
However, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun, relative to Earth. From this vantage point, the distance between Earth and the Asteroid Blt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges between being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.
But of course, for reasons of fuel economy and time, asteroid miners and exploration missions are not about to take the long way! As such, we can safely assume that the distance between Earth and the Asteroid Belt when they are at their closest is the only measurement worth considering.
Past Missions:
The Asteroid Belt is so thinly populated that several unmanned spacecraft have been able to move through it on their way to the outer Solar System. In more recent years, missions to study larger Asteroid Belt objects have also used this to their advantage, navigating between the smaller objects to rendezvous with bodies like Ceres and Vesta. In fact, due to the low density of materials within the Belt, the odds of a probe running into an asteroid are now estimated at less than one in a billion.
The first spacecraft to make a journey through the asteroid belt was the Pioneer 10 spacecraft, which entered the region on July 16th, 1972 (a journey of 135 days). As part of its mission to Jupiter, the craft successfully navigated through the Belt and conducted a flyby of Jupiter (in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.
An artist’s illustration of NASA’s Dawn spacecraft approaching Ceres. Image: NASA/JPL-Caltech.
For the most part, these missions were part of missions to the outer Solar System, where opportunities to photograph and study asteroids were brief. Only the Dawn, NEAR and JAXA’s Hayabusamissions have studied asteroids for a protracted period in orbit and at the surface. Dawn explored Vesta from July 2011 to September 2012, and is currently orbiting Ceres (and sending back gravity data on the dwarf planet’s gravity) and is expected to remain there until 2017.
Fastest Mission to Date:
The fastest mission humanity has ever mounted was the New Horizons mission, which was launched from Earth on Jan. 19th, 2006. The mission began with a speedy launch aboard an Atlas V rocket, which accelerated it to a a speed of about 16.26 km per second (58,536 km/h; 36,373 mph). At this speed, the probe reached the Asteroid Belt by the following summer, and made a close approach to the tiny asteroid 132524 APL by June 13th, 2006 (145 days after launching).
However, even this pales in comparison to Voyager 1, which was launched on Sept. 5th, 1977 and reached the Asteroid Belt on Dec. 10th, 1977 – a total of 96 days. And then there was the Voyager 2 probe, which launched 15 days after Voyager 1 (on Sept. 20th), but still managed to arrive on the same date – which works out to a total travel time of 81 days.
For Voyager 2, out on the edge of our Solar system, conventional navigation methods don’t work too well. Credit: NASA
Not bad as travel times go. At these speed, a spacecraft could make the trip to the Asteroid Belt, spend several weeks conducting research (or extracting ore), and then make it home in just over six months time. However, one has to take into account that in all these cases, the mission teams did not decelerate the probes to make a rendezvous with any asteroids.
Ergo, a mission to the Asteroid Belt would take longer as the craft would have to slow down to achieve orbital velocity. And they would also need some powerful engines of their own in order to make the trip home. This would drastically alter the size and weight of the spacecraft, which would inevitably mean it would be bigger, slower and a heck of a lot more expensive than anything we’ve sent so far.
Another possibility would be to use ionic propulsion (which is much more fuel efficient) and pick up a gravity assist by conducting a flyby of Mars – which is precisely what the Dawn mission did. However, even with a boost from Mars’ gravity, the Dawn mission still took over three years to reach the asteroid Vesta – launching on Sept. 27th, 2007, and arriving on July 16th, 2011, (a total of 3 years, 9 months, and 19 days). Not exactly good turnaround!
Proposed Future Methods:
A number of possibilities exist that could drastically reduce both travel time and fuel consumption to the Asteroid Belt, many of which are currently being considered for a number of different mission proposals. One possibility is to use spacecraft equipped with nuclear engines, a concept which NASA has been exploring for decades.
The Crew Transfer Vehicle (CTV) using its nuclear-thermal rocket engines to slow down and establish orbit around Mars. Credit: NASA
In a Nuclear Thermal Propulsion (NTP) rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust. A Nuclear Electric Propulsion (NEP) rocket involves the same basic reactor converting its heat and energy into electrical energy, which would then power an electrical engine.
In both cases, the rocket would rely on nuclear fission or fusion to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date. According to NASA estimates, the most sophisticated NTP concept would have a maximum specific impulse of 5000 seconds (50 kN·s/kg).
Using this engine, NASA scientists estimate that it would take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth. Adjusted for a distance of 1.2 AUs, that means that a ship equipped with a NTP/NEC propulsion system could make the trip in about 293 days (about nine months and three weeks). A little slow, but not bad considering the technology exists.
Another proposed method of interstellar travel comes in the form of the Radio Frequency (RF) Resonant Cavity Thruster, also known as the EM Drive. Originally proposed in 2001 by Roger K. Shawyer, a UK scientist who started Satellite Propulsion Research Ltd (SPR) to bring it to fruition, this drive is built around the idea that electromagnetic microwave cavities can allow for the direct conversion of electrical energy to thrust.
Artist’s concept of an interstellar craft equipped with an EM Drive. Credit: NASA Spaceflight Center
According to calculations based on the NASA prototype (which yielded a power estimate of 0.4 N/kilowatt), a spacecraft equipped with the EM drive could make the trip to Mars in just ten days. Adjusted for a trip to the Asteroid Belt, so a spacecraft equipped with an EM drive would take an estimated 32.5 days to reach the Asteroid Belt.
Impressive, yes? But of course, that is based on a concept that has yet to be proven. So let’s turn to yet another radical proposal, which is to use ships equipped with an antimatter engine. Created in particle accelerators, antimatter is the most dense fuel you could possibly use. When atoms of matter meet atoms of antimatter, they annihilate each other, releasing an incredible amount of energy in the process.
According to the NASA Institute for Advanced Concepts (NIAC), which is researching the technology, it would take just 10 milligrams of antimatter to propel a human mission to Mars in 45 days. Based on this estimate, a craft equipped with an antimatter engine and roughly twice as much fuel could make the trip to the Asteroid Belt in roughly 147 days. But of course, the sheer cost of creating antimatter – combined with the fact that an engine based on these principles is still theoretical at this point – makes it a distant prospect.
Basically, getting to the Asteroid Belt takes quite a bit of time, at least when it comes to the concepts we currently have available. Using theoretical propulsion concepts, we are able to cut down on the travel time, but it will take some time (and lots of money) before those concepts are a reality. However, compared to many other proposed missions – such as to Europa and Enceladus – the travel time is shorter, and the dividends quite clear.
As already stated, there are enough resources – in the form of minerals and volatiles – in the Asteroid Belt to last us indefinitely. And, should we someday find a way to cost-effective way to send spacecraft there rapidly, we could tap that wealth and begin to usher in an age of post-scarcity! But as with so many other proposals and mission concepts, it looks like we’ll have to wait for the time being.
Artist's impression of the asteroid belt. Image credit: NASA/JPL-Caltech
In the 18th century, observations made of all the known planets (Mercury, Venus, Earth, Mars, Jupiter and Saturn) led astronomers to the realization that there was a pattern in their orbits. Eventually, this led to the Titius–Bode law, which predicted the amount of space that naturally existed between each celestial body that orbited our Sun. In accordance with this law, astronomers noted that there appeared to be a discernible gap between the orbits of Mars and Jupiter.
Investigations into this gap eventually resulted in astronomers observing several bodies of various size. This led to the creation of the term “asteroid” (Greek for ‘star-like’ or ‘star-shaped’), as well as “Asteroid Belt”, once it became clear just how many there were. Through various methods, astronomers have since confirmed the existence of several million objects between the orbit of Mars and Jupiter. They have also determined, with a certain degree of accuracy, how far it is from our planet.
Structure and Composition:
The Asteroid Belt consists of several large bodies, coupled with millions of smaller size. The larger bodies, such as Ceres, Vesta, Pallas, and Hygiea, account for half of the belt’s total mass, with almost one-third accounted for by Ceres alone. Beyond that, over 200 asteroids that are larger than 100 km in diameter, and 0.7–1.7 million asteroids with a diameter of 1 km or more.
The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons
It total, the Asteroid Belt’s mass is estimated to be 2.8×1021 to 3.2×1021 kilograms – which is equivalent to about 4% of the Moon’s mass. While most asteroids are composed of rock, a small portion of them contain metals such as iron and nickel. The remaining asteroids are made up of a mix of these, along with carbon-rich materials. Some of the more distant asteroids tend to contain more ices and volatiles, which includes water ice.
Despite the impressive number of objects contained within the belt, the Main Belt’s asteroids are also spread over a very large volume of space. As a result, the average distance between objects is roughly 965,600 km (600,000 miles), meaning that the Main Belt consists largely of empty space. In fact, due to the low density of materials within the Belt, the odds of a probe running into an asteroid are now estimated at less than one in a billion.
The main (or core) population of the asteroid belt is sometimes divided into three zones, which are based on what is known as “Kirkwood gaps”. Named after Daniel Kirkwood, who announced in 1866 the discovery of gaps in the distance of asteroids, these gaps are similar to what is seen with Saturn’s and other gas giants’ systems of rings.
Orbit Around the Sun:
Located between Mars and Jupiter, the belt ranges in distance between 2.2 and 3.2 astronomical units (AU) from the Sun – 329 million to 478.7 million km (204.43 million to 297.45 million mi). It is also an estimated 1 AU thick (149.6 million km, or 93 million mi), meaning that it occupies the same amount of distance as what lies between the Earth to the Sun.
The distance of an asteroid from the Sun (its semi-major axis) depends upon its distribution into one of three different zones based on the Belt’s “Kirkwood Gaps”. Zone I lies between the 4:1 resonance and 3:1 resonance Kirkwood gaps, which are roughly 2.06 and 2.5 AUs (3 to 3.74 billion km; 1.86 to 2.3 billion mi) from the Sun, respectively.
Zone II continues from the end of Zone I out to the 5:2 resonance gap, which is 2.82 AU (4.22 billion km; 2.6 mi) from the Sun. Zone III, the outermost section of the Belt, extends from the outer edge of Zone II to the 2:1 resonance gap, located some 3.28 AU (4.9 billion km; 3 billion mi) from the Sun.
Distance from Earth:
The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the closest edge of the Belt can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi). But of course, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun relative to us as well.
From this vantage point, the distance between Earth and the Asteroid Belt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges from being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.
Naturally, any exploration or other kind of mission launched from Earth is going to take the shortest route, unless it is aiming for a specific asteroid. And even then, mission planners will time the launch to ensure that we are closest to the destination. Hence, we can safely use the estimates of 1.2 – 2.2 AU to gauge the distance between us and the Main Belt.
Even so, at its closest, getting to the Asteroid Belt would involve a bit of a hike! In short, it is approximately 179.5 million km (or 111.5 million mi) distant from us at any given time. As such, knowing just how much time and energy it would take to get their and back is going to come in handy if and when we begin mounting crewed missions to the Belt, not to mention the prospect of asteroid mining!
In a previous article, we crushed that idea that the Universe is perfect for life. It’s not. Almost the entire Universe is a horrible and hostile place, apart from a fraction of a mostly harmless planet in a backwater corner of the Milky Way.
While living here on Earth takes about 80 years to kill you, there are other places in the Universe at the very other end of the spectrum. Places that would kill you in a fraction of a fraction of a second. And nothing is more lethal than supernovae and remnants they leave behind: neutron stars.
We’ve done a few articles about neutron stars and their different flavours, so there should be some familiar terrain here.
Artist concept of a neutron star. Credit: NASA
As you know, neutron stars are formed when stars more massive than our Sun explode as supernovae. When these stars die, they no longer have the light pressure pushing outward to counteract the massive gravity pulling inward.
This enormous inward force is so strong that it overcomes the repulsive force that keeps atoms from collapsing. Protons and electrons are forced into the same space, becoming neutrons. The whole thing is just made of neutrons. Did the star have hydrogen, helium, carbon and iron before? That’s too bad, because now it’s all neutrons.
You get pulsars when neutron stars first form. When all that former star is compressed into a teeny tiny package. The conservation of angular motion spins the star up to tremendous velocities, sometimes hundreds of times a second.
But when neutron stars form, about one in ten does something really really strange, becoming one of the most mysterious and terrifying objects in the Universe. They become magnetars. You’ve probably heard the name, but what are they?
As I said, magnetars are neutron stars, formed from supernovae. But something unusual happens as they form, spinning up their magnetic field to an intense level. In fact, astronomers aren’t exactly sure what happens to make them so strong.
This artist’s impression shows the magnetar in the very rich and young star cluster Westerlund 1. Credit: ESO/L. Calçada
One idea is that if you get the spin, temperature and magnetic field of a neutron star into a perfect sweet spot, it sets off a dynamo mechanism that amplifies the magnetic field by a factor of a thousand.
But a more recent discovery gives a tantalizing clue for how they form. Astronomers discovered a rogue magnetar on an escape trajectory out of the Milky Way. We’ve seen stars like this, and they’re ejected when one star in a binary system detonates as a supernova. In other words, this magnetar used to be part of a binary pair.
And while they were partners, the two stars orbited one another closer than the Earth orbits the Sun. This close, they could transfer material back and forth. The larger star began to die first, puffing out and transferring material to the smaller star. This increased mass spun the smaller star up to the point that it grew larger and spewed material back at the first star.
The initially smaller star detonated as a supernova first, ejecting the other star into this escape trajectory, and then the second went off, but instead of forming a regular neutron star, all these binary interactions turned it into a magnetar. There you go, mystery maybe solved?
The strength of the magnetic field around a magnetar completely boggles the imagination. The magnetic field of the Earth’s core is about 25 gauss, and here on the surface, we experience less than half a gauss. A regular bar magnet is about 100 gauss. Just a regular neutron star has a magnetic field of a trillion gauss. Magnetars are 1,000 times more powerful than that, with a magnetic field of a quadrillion gauss.
What if you could get close to a magnetar? Well, within about 1,000 kilometers of a magnetar, the magnetic field is so strong it messes with the electrons in your atoms. You would literally be torn apart at an atomic level. Even the atoms themselves are deformed into rod-like shapes, no longer usable by your precious life’s chemistry.
But you wouldn’t notice because you’d already be dead from the intense radiation streaming from the magnetar, and all the lethal particles orbiting the star and trapped in its magnetic field.
Artist’s conception of a starquake cracking the surface of a neutron star. Credit: Darlene McElroy of LANL
One of the most fascinating aspects of magnetars is how they can have starquakes. You know, earthquakes, but on stars… starquakes. When neutron stars form, they can have a delicious murder crust on the outside, surrounding the degenerate death matter inside. This crust of neutrons can crack, like the tectonic plates on Earth. As this happens, the magnetar releases a blast of radiation that we can see clear across the Milky Way.
In fact, the most powerful starquake ever recorded came from a magnetar called SGR 1806-20, located about 50,000 light years away. In a tenth of a second, one of these starquakes released more energy than the Sun gives off in 100,000 years. And this wasn’t even a supernova, it was merely a crack on the magnetar’s surface.
Magnetars are awesome, and provide the absolute opposite end of the spectrum for a safe and habitable Universe. Fortunately, they’re really far away and you won’t have to worry about them ever getting close.
Artist's concept of KIC 8462852, which has experienced unusual changes in luminosity over the past few years. Credit: NASA, JPL-Caltech
Last fall, astronomers were surprised when the Kepler mission reported some anomalous readings from KIC 8462852 (aka. Tabby’s Star). After noticing a strange and sudden drop in brightness, speculation began as to what could be causing it – with some going so far as to suggest that it was an alien megastructure. Naturally, the speculation didn’t last long, as further observations revealed no signs of intelligent life or artificial structures.
But the mystery of the strange dimming has not gone away. What’s more, in a paper posted this past Friday to arXiv, Benjamin T. Montet and Joshua D. Simon (astronomers from the Cahill Center for Astronomy and Astrophysics at Caltech and the Carnegie Institute of Science, respectively) have shown how an analysis of the star’s long-term behavior has only deepened the mystery further.
To recap, dips in brightness are quite common when observing distant stars. In fact, this is one of the primary techniques employed by the Kepler mission and other telescopes to determine if planets are orbiting a star (known as Transit Method). However, the “light curve” of Tabby’s Star – named after the lead author of the study that first detailed the phenomena (Tabetha S. Boyajian) – was particularly pronounced and unusual.
Freeman Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
According to the study, the star would experience a ~20% dip in brightness, which would last for between 5 and 80 days. This was not consistent with a transitting planet, and Boyajian and her colleagues hypothesized that it was due to a swarm of cold, dusty comet fragments in a highly eccentric orbit accounted for the dimming.
However, others speculated that it could be the result of an alien megastructure known as Dyson Sphere (or Swarm), a series of structures that encompass a star in whole or in part. However, the SETI Institute quickly weighed in and indicated that radio reconnaissance of KIC 8462852 found no evidence of technology-related radio signals from the star.
Other suggestions were made as well, but as Dr. Simon of the Carnegie Institute of Science explained via email, they fell short. “Because the brief dimming events identified by Boyajian et al. were unprecedented, they sparked a wide range of ideas to explain them,” he said. “So far, none of the proposals have been very compelling – in general, they can explain some of the behavior of KIC 8462852, but not all of it.”
To put the observations made last Fall into a larger context, Montet and Simon decided to examine the full-frame photometeric images of KIC 8462852 obtained by Kepler over the last four years. What they found was that the total brightness of the star had been diminishing quite astonishingly during that time, a fact which only deepens the mystery of the star’s light curve.
Photometry of KIC8462852 obtained by the Kepler mission, showing a period of more rapid decline during the later period of observation. Credit: Montet & Simon 2016
As Dr. Montet told Universe Today via email:
“Every 30 minutes, Kepler measures the brightness of 160,000 stars in its field of view (100 square degrees, or approximately as big as your hand at arm’s length). The Kepler data processing pipeline intentionally removes long-term trends, because they are hard to separate from instrumental effects and they make the search for planets harder. Once a month though, they download the full frame, so the brightness of every object in the field can be measured. From this data, we can separate the instrumental effects from astrophysical effects by seeing how the brightness of any particular star changes relative to all its neighboring stars.”
Specifically, they found that over the course of the first 1000 days of observation, the star experienced a relatively consistent drop in brightness of 0.341% ± 0.041%, which worked out to a total dimming of 0.9%. However, during the next 200 days, the star dimmed much more rapidly, with its total stellar flux dropping by more than 2%.
For the final 200 days, the star’s magnitude once again consistent and similar to what it was during the first 1000 – roughly equivalent to 0.341%. What is impressive about this is the highly anomalous nature of it, and how it only makes the star seem stranger. As Simon put it:
“Our results show that over the four years KIC 8462852 was observed by Kepler, it steadily dimmed. For the first 2.7 years of the Kepler mission the star faded by about 0.9%. Its brightness then decreased much faster for the next six months, declining by almost 2.5% more, for a total brightness change of around 3%. We haven’t yet found any other Kepler stars that faded by that much over the four-year mission, or that decreased by 2.5% in six months.”
Artist’s conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech
Of the over 150,000 stars monitored by the Kepler mission, Tabby’s Starr is the only one known to exhibit this type of behavior. In addition, Monetet and Cahill compared the results they obtained to data from 193 nearby stars that had been observed by Kepler, as well as data obtained on 355 stars with similar stellar parameters.
From this rather large sampling, they found that a 0.6% change in luminosity over a four year period – which worked out to about 0.341% per year – was quite common. But none ever experienced the rapid decline of more than 2% that KIC 8462852 experienced during that 200 days interval, or the cumulative fading of 3% that it experienced overall.
Montet and Cahill looked for possible explanations, considering whether the rapid decline could be caused by a cloud of transiting circumstellar material. But whereas some phenomena can explain the long-term trend, and other the short-term trend, no one explanation can account for it all. As Montet explained:
“We propose in our paper that a cloud of gas and dust from the remnants of a planetesimal after a collision in the outer solar system of this star could explain the 2.5% dip of the star (as it passes along our line of sight). Additionally, if some clumps of matter from this collision were collided into high-eccentricity comet-like orbits, they could explain the flickering from Boyajian et al., but this model doesn’t do a nice job of explaining the long-term dimming. Other researchers are working to develop different models to explain what we see, but they’re still working on these models and haven’t submitted them for publication yet. Broadly speaking, all three effects we observe cannot be explained by any known stellar phenomenon, so it’s almost certainly the result of some material along our line of sight passing between us and the star. We just have to figure out what!”
So the question remains, what accounts for this strange dimming effect around this star? Is there yet some singular stellar phenomena that could account for it all? Or is this just the result of good timing, with astronomers being fortunate enough to see a combination of a things at work in the same period? Hard to say, and the only way we will know for sure is to keep our eye on this strangely dimming star.
And in the meantime, will the alien enthusiasts not see this as a possible resolution to the Fermi Paradox? Most likely!
A brilliant early Perseid meteor from the night of August 8th over Cabo Rojo, Puerto Rico. Image credit and copyright: Frankie Lucena.
Out camping under the August sky? The coming week gives us a good reason to stay up late, as the Perseid meteor shower graces the summer sky. An ‘old faithful’ of annual meteor showers, the Perseids are always sure to produce.
The 2016 Perseids present a few challenges, though persistent observers should still see a descent show. The Perseids are typically active from July 17th to August 24th, with the peak arriving this year right around 13:00 to 15:30 Universal Time on Friday, August 12th. This will place the radiant for the Perseids high in the sky after local midnight for observers in the northern Pacific, though observers worldwide should be vigilant over the next week. Meteor showers don’t read predictions and prognostications, and an arrival of the peak just a few hours early would place North America in the cross-hairs this coming Friday. The Perseids typically produce an average Zenithal Hourly Rate of 60-200 per hour, and the International Meteor Organization predicts a ZHR of 150 for 2016.
Looking to the northeast from latitude 50 degrees north at 1AM local on the morning of August 12th. Image credit: Stellarium.
The nemesis of the 2016 is the Moon, which reaches Full on August 18th, six days after the shower’s peak. The time to start watching this shower is now, before the waxing Moon becomes a factor. The farther north you are, the earlier the Moon sets this week:
Moonset on the evening of August 11/12th:
Latitude versus Moonset ( in local daylight saving time)
20 degrees north – 1:30 AM
30 degrees north – 1:14 AM
40 degrees north – 0:56 AM
50 degrees north – 0:30 AM
Early morning is almost always the best time to watch any meteor shower, as the Earth-bound observer faces in to the meteor stream head on. The December Geminids only recently surpassed the Perseids in annual intensity in the past few years.
The orientation of the Earth’s shadow versus the Sun, Moon and the radiant of the Perseids at the start of the projected peak on August 12th. Image credit: Orbitron.
The radiant of the Perseids drifts through the constellations of Cassiopeia, Perseus and Camelopardalis from late July to mid-August. The Perseids could just as easily have received the tongue-twisting moniker of the ‘Cassiopeiaids’ or the ‘August Camelopardalids.’ The source of the Perseids is comet Comet 109P/Swift-Tuttle discovered by Lewis Swift and Horace Tuttle in 1862. Comet Swift-Tuttle reached perihelion on 1992, and visits the inner solar system once again in 2126.
The Perseids are also sometimes referred as the “Tears of Saint Lawrence” who was martyred on a hot grid iron on August 10th, 258 AD.
The Perseids have been especially active in recent decades, following the perihelion passage of Comet Swift-Tuttle. Meteor showers come and go. For example, the Andromedids were a shower of epic storm proportions until the late 19th century. We have records of the Perseids back to 36AD, but on some (hopefully) far off date, the debris path of Comet Swift-Tuttle will fail to intersect the Earth’s orbit annually, and the Perseids will become a distant memory. During previous years, the Perseids exhibited a peak of ZHR= 95 (2015), 68 (2014), 110 (2013), 121 (2012) and 58 (2011). Keep in mind, the Perseids have also sometimes displayed a twin peak during previous years, as well.
The best instrument to observe the Perseids with is a pair of old fashioned, ‘Mk-1 eyeballs.’ Simply lay back, warm drink in hand, and watch. Remember, the quoted ZHR is an ideal rate that we all strive for, though there are strategies to maximize your chances of catching a meteor. Watching early in the morning when the radiant rides highest (around sunrise in the case of the Perseids), seeking out dark skies, and enlisting a friend to watch in an opposite direction can raise your hourly meteor count.
An early Perseid captured by Chris-Lyons. Image credit and copyright: Chris Lyons.
Keep a pair of binoculars handy to examine any persistent glowing trains and lingering smoke trails from bright fireballs. Monitoring the FM band for the pings of accompanying radio meteors can add another dimension to an observation session. The ionized trail of a meteor can very occasionally reflect the signal of a distant radio station, bringing it through clear for a few seconds before fading out.
Also, keep an ear out for an even stranger phenomenon, as bright meteors are sometimes accompanied by a hissing or crackling sound. Long thought to be a psychological phenomenon, a team of Japanese astronomers managed to catch recordings of this strange effect during the 1988 Perseid meteors.
Imaging meteors is also pretty straight forward. Simply tripod mount a DSLR with a wide field lens, take some test exposures of the sky to get the ISO, f-stop and exposure combination just right, and begin taking exposures 30 seconds to five minutes long. An intervalometer can automate the process, freeing you up to kick back and watch the show.
