This artist’s rendering shows the Extremely Large Telescope in operation on Cerro Armazones in northern Chile. The telescope is shown using lasers to create artificial stars high in the atmosphere. Image: ESO/E-ELT
The construction of the world’s largest telescope has begun. At a ceremony at the European Southern Observatory’s (ESO) Paranal Observatory in Chile, officials gathered to celebrate the first stone of the European Extremely Large Telescope’s (E-ELT) long-awaited construction. Sophisticated telescope projects like the E-ELT take many years, so we can expect another similar ceremony sometime in 2021, when the E-ELT will see first light.
The E-ELT is the ESO’s flagship observatory. It’s primary mirror will be a 39.3 meter (129 ft.) monstrosity that will observe in the visible, near-infrared, and mid-infrared spectra. The construction of the site began in 2014, but this ceremony marks the beginning of the construction of the main telescope and its dome. The ceremony also marks the connection of the telescope to the electricity grid.
The Chilean President, Michelle Bachelet Jeria, attended the ceremony. She was welcomed by the Director General of ESO Tim de Zeeuw, by ELT Programme Manager Roberto Tamai, and by other officials from the ESO. Staff from the La Silla Paranal Observatory, and numerous engineers and technicians—as well as numerous representatives from Chilean government and industry—also attended the ceremony.
“With the symbolic start of this construction work, we are building more than a telescope here.” – President of the Republic of Chile, Michelle Bachelet Jeria
In her speech, the President spoke in favor of the E-ELT, and in support of science and cooperation. “With the symbolic start of this construction work, we are building more than a telescope here: it is one of the greatest expressions of scientific and technological capabilities and of the extraordinary potential of international cooperation.”
At the ceremony, a time capsule from ESO was sealed into place. The capsule is a hexagon shaped, one-fifth scale model of the E-ELT containing a poster made of photographs of current ESO staff, and a copy of the book detailing the E-ELT’s science goals.
The first stone ceremony is definitely an important milestone for this Super Telescope, but it’s just one of the milestones reached by the E-ELT in the past two weeks.
The secondary mirror for the E-ELT has already been cast. At 4.2 meters in diameter, it is the largest secondary mirror ever used on an an optical telescope. Image: ESO/Schott.
The secondary mirror for the E-ELT has already been cast, and the ESO has announced that the contracts for the primary mirror have now been signed. The primary mirror segment blanks, all 798 of them, will be made by the Germany company SCHOTT. Once produced, they will be polished by the French company Safran Reosc. Safran Reosc will also mount and test the mirror segments.
“This has been an extraordinary two weeks!” – Tim de Zeeuw, European Southern Observatory’s Director General
Tim de Zeeuw, ESO’s Director General, is clearly excited about the progress being made on the E-ELT. At the contract signing, de Zeeuw said, “This has been an extraordinary two weeks! We saw the casting of the ELT’s secondary mirror and then, last Friday, we were privileged to have the President of Chile, Michelle Bachelet, attend the first stone ceremony of the ELT. And now two world-leading European companies are starting work on the telescope’s enormous main mirror, perhaps the biggest challenge of all.”
This artist’s rendering shows the huge segmented primary mirror of the ESO Extremely Large Telescope (ELT). Contracts for the manufacture of the mirror segments were signed on 30 May 2017. Image: ESO/L. Calcada
It’s taken an enormous amount of work to get to the construction stage of the world’s largest telescope. Scientist’s, engineers, and technicians have been working for years to get this far. But without the contribution of Chile, none of it would happen. Chile is the world’s astronomy capital, and they continue working with the ESO and other nations to drive scientific discovery forward.
The E-ELT has three broad-based science objectives. It will:
Probe Earth-like exoplanets for signs of life
Study the nature of dark energy and dark matter
Observe the Universe’s early stages to understand our origins and the origin of galaxies and solar systems
Along the way, it will no doubt raise new questions that we can’t even imagine yet.
Artistic design of the super-Earth GJ 625 b and its star, GJ625 (Gliese 625). Credit: Gabriel Pérez/SMM (IAC)
M-type stars, also known as “red dwarfs”, have become a popular target for exoplanet hunters of late. This is understandable given the sheer number of terrestrial (i.e. rocky) planets that have been discovered orbiting around red dwarf stars in recent years. These discoveries include the closest exoplanet to our Solar System (Proxima b) and the seven planets discovered around TRAPPIST-1, three of which orbit within the star’s habitable zone.
The latest find comes from a team of international astronomers who discovered a planet around GJ 625, a red dwarf star located just 21 light years away from Earth. This terrestrial planet is roughly 2.82 times the mass of Earth (aka. a “super-Earth”) and orbits within the star’s habitable zone. Once again, news of this discovery is prompting questions about whether or not this world could indeed be habitable (and also inhabited).
Diagram showing GJ 625’s habitable zone in comparison’s to the Sun’s. Credit: IAC
The study which details their findings was recently accepted for publication by the journal Astronomy & Astrophysics, and appears online under the title “A super-Earth on the Inner Edge of the Habitable Zone of the Nearby M-dwarf GJ 625“. According to the study, the team used radial-velocity measurements of GJ 625 in order to determine the presence of a planet that has between two and three times the mass of Earth.
Using this instrument, the team collected high-resolution spectroscopic data of the GJ 625 system over the course of three years. Specifically, they measured small variations in the stars radial velocity, which are attributed to the gravitational pull of a planet. From a total of 151 spectra obtained, they were able to determine that the planet (GJ 625 b) was likely terrestrial and had a minimum mass of 2.82 ± 0.51 Earth masses.
Moreover, they obtained distance estimates that placed it roughly 0.078 AU from its star, and an orbital period estimate of 14.628 ± 0.013 days. At this distance, the planet’s orbit places it just within GJ 625’s habitable zone. Of course, this does not mean conclusively that the planet has conditions conducive to life on its surface, but it is an encouraging indication.
Tjhe Observatorio del Roque de los Muchachos, located on the island of La Palma. Credit: IAC
As Alejandro Suárez Mascareño explained in an IAC press release:
“As GJ 625 is a relatively cool star the planet is situated at the edge of its habitability zone, in which liquid water can exist on its surface. In fact, depending on the cloud cover of its atmosphere and on its rotation, it could potentially be habitable”.
This is not the first time that the HADES project detected an exoplanet around a red dwarf star. In fact, back in 2016, a team of international researchers used this project to discover 2 super-Earths orbiting GJ 3998, a red dwarf located about 58 ± 2.28 light years from Earth. Beyond HADES, this discovery is yet another in a long line of rocky exoplanets that have been discovered in the habitable zone of a nearby red dwarf star.
Such findings are very encouraging since red dwarfs are the most common type of star in the known Universe- accounting for an estimated 70% of stars in our galaxy alone. Combined with the fact that they can exist for up to 10 trillion years, red dwarf systems are considered a prime candidate in the search for habitable exoplanets.
But as with all other planets discovered around red dwarf stars, there are unresolved questions about how the star’s variability and stability could affect the planet. For starters, red dwarf stars are known to vary in brightness and periodically release gigantic flares. In addition, any planet close enough to be within the star’s habitable zone would likely be tidally-locked with it, meaning that one side would be exposed to a considerable amount of radiation.
Artist’s impression of of the exoplanets orbiting a red dwarf star. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).
As such, additional observations will need to be made of this exoplanet candidate using the time-tested transit method. According to Jonay Hernández – a professor from the University of La Laguna, a researcher with the IAC and one of the co-authors on the study – future studies using this method will not only be able to confirm the planet’s existence and characterize it, but also determine if there are any other planets in the system.
“In the future, new observing campaigns of photometric observations will be essential to try to detect the transit of this planet across its star, given its proximity to the Sun,” he said. “There is a possibility that there are more rocky planets around GJ 625 in orbits which are nearer to, or further away from the star, and within the habitability zone, which we will keep on combing”.
According to Rafael Rebolo – one of the study’s co-authors from the Univeristy of La Laguna, a research with the IAC, and a member of the CSIS – future surveys using the transit method will also allow astronomers to determine with a fair degree of certainty whether or not GJ 625 b has the all-important ingredient for habitability – i.e. an atmosphere:
“The detection of a transit will allow us to determine its radius and its density, and will allow us to characterize its atmosphere by the transmitted light observe using high resolution high stability spectrographs on the GTC or on telescopes of the next generation in the northern hemisphere, such as the Thirty Meter Telescope (TMT)”.
Artist’s impression of a system of exoplanets orbiting a low mass, red dwarf star. Credit: NASA/JPL
But what is perhaps most exciting about this latest find is how it adds to the population of extra-solar planets within our cosmic neighborhood. Given their proximity, each of these planets represent a major opportunity for research. And as Dr. Mascareño told Universe Today via email:
“While we have already found more than 3600 extra-solar planets, the exoplanet population in our near neighborhood is still somewhat unknown. At 21 ly from the Sun, GJ 625 is one of the 100 nearest stars, and right now GJ 625 b is one of the 30 nearest exoplanets detected and the 6th nearest potentially habitable exoplanet.”
Once again, ongoing surveys of nearby star systems is providing plenty of potential targets in the search for life beyond our Solar System. And with both ground-based and space-based next-generation telescopes joining the search, we can expect to find many, many more candidates in the coming years. In the meantime, be sure to check out this animation of GJ 625 b and its parent star:
The first wild back-and-forth line records the moment (October 13, 2014 at 21:18:48.404 UTC) that the left NAC radiator was struck by a meteoroid. Credit: NASA/GSFC/Arizona State University
On October 13th, 2014, the Lunar Reconnaissance Orbiter (LRO) experienced something rare and unexpected. While monitoring the surface of the Moon, the LRO’s main instrument – the Lunar Reconnaissance Orbiter Camera (LROC) – produced an image that was rather unusual. Whereas most of the images it has produced were detailed and exact, this one was subject to all kinds of distortion.
From the way this image was disturbed, the LRO science team theorized that the camera must have experienced a sudden and violent movement. In short, they concluded that it had been struck by a tiny meteoroid, which proved to a significant find in itself. Luckily, the LRO and its camera appear to have survived the impact unharmed and will continue to survey the surface of the Moon for years to come.
The LROC is a system of three cameras that are mounted aboard the LRO spacecraft. This include two Narrow Angle Cameras (NACs) – which capture high-resolution black and white images – and a third Wide Angle Camera (WAC), which captures moderate resolution images that provide information about the properties and color of the lunar surface.
The NAC on a bench in the clean room at Malin Space Science Systems. Credit: Courtesy of Malin Space Science Systems/ASU SESE
The NACs works by building an image one line at a time, with thousands of lines being used to compile a full image. In between the capture process, the spacecraft moves the camera relative to the surface. On October 13th, 2014, at precisely 21:18:48 UTC, the camera added a line that was visibly distorted. This sent the LRO team on a mission to investigate what could have caused it.
Led by Mark Robinson – a professor and the principal investigator of the LROC at Arizona State University’s School of Earth and Space Exploration – the LROC researchers concluded that the left Narrow Angle Camera must have experienced a brief and violent movement. As there were no spacecraft events – like a solar panel movement or antenna tracking – that might have caused this, the only possibility appeared to be a collision.
As Robinson explained in a recent post on the LROC’s website:
“There were no spacecraft events (such as slews, solar panel movements, antenna tracking, etc.) that might have caused spacecraft jitter during this period, and even if there had been, the resulting jitter should have affected both cameras identically… Clearly there was a brief violent movement of the left NAC. The only logical explanation is that the NAC was hit by a meteoroid! How big was the meteoroid, and where did it hit?”
To test this, the team used a detailed computer model that was developed specifically for the LROC to ensure that the NAC would not fail during the launch of the spacecraft, when severe vibrations would occur. With this model, the LROC team ran simulations to see if they could reproduce the distortions that would have caused the image. Not only did they conclude it was the result of a collision, but they were also able to determine the size of the meteoroid that hit it.
LROC Narrow Angle Camera (NAC). Credit: ASU/LROC SESE
The results indicated that the impacting meteoroid would have measured about 0.8 mm in diameter and had a density of a regular chondrite meteorite (2.7 g/cm³). What’s more, they were able to estimate that it was traveling at a velocity of about 7 km/s (4.3 miles per second) when it collided with the NAC. This was rather surprising, given the odds of collisions and how much time the LRO spends gathering data.
Typically, the LROC only captures images during daylight hours, and for about 10% of the day. So for it to have been hit while it was also capturing images is statistically unlikely – only about 5% by Robinson’s own estimate. Luckily, the impact has not caused any technical problems for the LROC, which is also something of a minor miracle. As Robinson explained:
“For comparison, the muzzle velocity of a bullet fired from a rifle is typically 0.5 to 1.0 kilometers per second. The meteoroid was traveling much faster than a speeding bullet. In this case, LROC did not dodge a speeding bullet, but rather survived a speeding bullet! LROC was struck and survived to keep exploring the Moon, thanks to Malin Space Science Systems’ robust camera design.”
It was only after the team deduced that no damage had been caused that prompted the announcement. According to John Keller, the LRO project scientist from NASA’s Goddard Space Flight Center, the real story here was how the imagery that was being acquired at the time was used to deduce how and when the LRO had been struck by a meteoroid.
Artist’s rendering of Lunar Reconnaissance Orbiter (LRO) in orbit. Credit: ASU/LROC
“Since the impact presented no technical problems for the health and safety of the instrument,” he said, “the team is only now announcing this event as a fascinating example of how engineering data can be used, in ways not previously anticipated, to understand what is happening to the spacecraft over 236,000 miles (380,000 kilometers) from the Earth.”
In addition, the impact of a meteoroid on the LRO demonstrates just how precious the information that missions like the LRO provides truly is. Beyond mapping the lunar surface, the orbiter was also able to let its science team know exactly and when its images were comprised, all because of the high-quality data it collects.
Since it launched in June of 2008, the LRO has collected an immense amount of data on the lunar surface. The mission has been extended several times, from its original duration of two years to the just under nine. Its ongoing performance is also a testament to the durability of the craft and its components.
Be sure to enjoy this video of the images obtained by the LRO, courtesy of the LROC team:
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at that buzzing nest of stars – the Beehive Cluster!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these is the Beehive Cluster (aka. Messier 44, or Praesepe), an open star cluster located in the the Cancer constellation. In addition to containing a larger population of stars than most clusters in its vicinity, it is also one of the nearest open clusters to the Solar System – at a distance of 577 light years (177 parsecs). As such, astronomers have been aware of it since Classical Antiquity.
Description:
According to ancient lore, this group of stars (often called the Praesepe) foretold a coming storm if it was not visible in otherwise clear skies. Of course, this came from a time when combating light pollution meant asking your neighbors to dim their candles. But, once you learn where it’s at, it can be spotted unaided even from suburban settings. Hipparchus called it the “Little Cloud,” but not until the early 1600s was its stellar nature revealed.
Close up of the Praesepe (Messier 44) open star cluster. Credit: Wikisky
Believed to be about 550 light-years away, this awesome cluster consists of hundreds of members – with at least four orange giants and five white dwarfs. M44’s age is similar to that of the Pleiades, and it is believed that both clusters have a common origin. Although you won’t see any nebulosity in the Beehive, even the very smallest of binoculars will reveal a swarm of bright stars and large telescopes can resolve down to 350 faint stars.
Messier 44 is the nearest open cluster of its type to our Solar System, and it contains a larger star population than most other nearby clusters. Under dark skies the Beehive Cluster looks like a nebulous object to the unaided eye; thus it has been known since ancient times. The classical astronomer Ptolemy called it “the nebulous mass in the heart of Cancer,” and it was among the first objects that Galileo studied with his telescope.
The cluster’s age and proper motion coincide with those of the Hyades stellar association, suggesting that both share a similar origin. Both clusters also contain red giants and white dwarfs, which represent later stages of stellar evolution, along with main sequence stars of spectral classes A, F, G, K, and M. So far, eleven white dwarfs have been identified, representing the final evolutionary phase of the cluster’s most massive stars, which originally belonged to spectral type B. Brown dwarfs, however, are extremely rare in this cluster, probably because they have been lost by tidal stripping from the halo.
Messier 44 is home to 5 red giant stars and a handful of white dwarf stars. But, M44 also contains one peculiar blue star. Among its members, there is the eclipsing binary TX Cancri, the metal line star Epsilon Cancri, and several Delta Scuti variables of magnitudes 7-8, in an early post-main-sequence state. And in all those stars, there’s a lot of other peculiarities to be found!
Atlas Image of the Beehive Cluster obtained as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/IPAC (Caltech)/NASA/NSF
As Sergei M. Andrievsky indicated in a 1998 study:
“We present the results of a spectroscopic study of four blue stragglers from old galactic open cluster NGC 2632 (Praesepe). The LTE analysis based on Kurucz’s atmosphere models and synthetic spectra technique has shown that three stars, including the hottest star of the cluster HD73666, possess an uniform chemical composition: they show a solar-like abundance (or slight overabundance) of iron and an apparent deficiency of oxygen and silicon. Two stars exhibit a remarkable barium overabundance. The chemical composition of their atmospheres is typical for Am stars. One star of our sample does not share such uniform elemental distribution, being generally deficient in metals.”
But is there more hiding in there? Perhaps the kind of stuff that could eventually make planets? According to a 2009 study done by A. Gaspar (et al), this was certainly thought to the be the case:
“Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. The incidence of excesses is in agreement with the decay trend of debris disks as a function of age observed for other cluster and field stars. We show that solar-type stars lose their debris disk 24 um excesses on a shorter timescale than early-type stars. Simplistic Monte Carlo models suggest that, during the first Gyr of their evolution, up to 15%-30% of solar-type stars might undergo an orbital realignment of giant planets such as the one thought to have led to the Late Heavy Bombardment, if the length of the bombardment episode is similar to the one thought to have happened in our solar system.”
In September of 2012, two planets were confirmed to be orbiting around two separate stars in the Beehive Cluster. The finding was significant since the stars were similar to Earth’s Sun, and this was the first instance where exoplanets were found orbiting a Sun-like star within a stellar cluster. These planets were designated as Pr0201b and Pr0211b, both of which are “Hot Jupiters” (i.e. gas giants that orbit close to their stars). In 2016, additional observations showed that the Pr0211 system actually has two planets, the second one being Pr0211-c.
History of Observation:
This beautiful, nearby star cluster has been known since ancient times and played wonderful roles in mythology. Aratos mentioned this object as “Little Mist” as far back as 260 BC, and Hipparchus included this object in his star catalog and called it “Little Cloud” or “Cloudy Star” in 130 BC. Ptolemy mentions it as one of seven “nebulae” he noted in his Almagest, and describes it as “The Nebulous Mass in the Breast (of Cancer)”.
According to Burnham, it appeared on Johann Bayer’s chart (about 1600 AD) as “Nubilum” (“Cloudy” Object). It was even resolved by Galileo in 1609 who said: “The nebula called Praesepe contains not one star only but a mass of more than 40 small stars. We have noted 36 besides the Aselli (Gamma and Delta Cancri).”
Messier 44 was partly resolved by Orion nebula’s discoverer, Peiresc, in 1611, who said, “Nebula was seen in the vicinity of Jupiter to the east. in which more than 15 stars have been counted.” and added to Hevelius’ catalog as number 291. De Cheseaux charted it as his number 11 and Bode as his number 20. Small wonder Messier felt the need to add his own numbers to it as well when he recorded:
“At simple view [with the naked eye], one sees in Cancer a considerable nebulosity: this is nothing but a cluster of many stars which one distinguishes very well with the help of telescopes, and these stars are mixed up at simple view [to the unaided eye] because of their great proximity. The position in right ascension of one of the stars, which Flamsteed has designated with the letter c, reduced to March 4, 1769, should be 126d 50′ 30″, for its right ascension, and 20d 31′ 38″ for its northern declination. This position is deduced from that which Flamsteed has given in his catalog.”
Image of M44 Beehive cluster taken by the author, Miguel Garcia. Credit: Intihuatana (Miguel Garcia)
While Sir William Herschel would ignore it and Caroline Herschel would only write that she “observed it”, John Herschel would go on to give it an NGC designation and Admiral Smyth would sing its poetic praises. Is it possible that watching this star cluster could help fortell the weather? If you believe the words of Aratos, it just might.
“Watch, too, the Manger. Like a faint mist in the North it plays the guide beneath Cancer. Around it are borne two faintly gleaming stars, not far apart nor very near but distant to the view a cubit.s length, one on the North, while the other looks towards the South. They are called the Asses [in the constellation Cancer], and between them is the Manger. On a sudden, when all the sky is clear, the Manger wholly disappears, while the stars that go on either side seem nearer drawn to one another: not slight then is the storm with which the fields are deluged. If the Manger darken and both stars remain unaltered, they herald rain. But if the Ass to the North of the Manger shine feebly through a faint mist, while the Southern Ass is gleaming bright, expect wind from the South: but if in turn the Southern Ass is cloudy and the Northern bright, watch for the North wind.”
And watch for a swarm of incredible starlight!
Locating Messier 44:
Messier 44 is so bright that it easily shows to the unaided eye as a nebulous patch just above the conjunction of the faint, upside down “Y” asterism of the Cancer constellation. However, not everyone lives where dark skies are a rule – so try using both Pollux and Procyon to form the base of an imaginary triangle. Now aim your binoculars or finderscope near the point of the apex to discover M44 – the Beehive.
The location of Messier 44 in the Cancer constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Since Messier 44 is about a degree and a half in diameter, it will require that you use your lowest magnification eyepiece in a telescope, and it is very well suited to binoculars of all sizes. Because its major stars are also quite bright, it stands up to urban sky and moonlight conditions, but many more stars are revealed with higher magnification and darker skies. Because M44 is very near the ecliptic plane, you’ll often find a planet or the Moon mixing it up with the stars!
Object Name: Messier 44 Alternative Designations: M44, NGC 2632, Beehive Cluster, The Praesepe, The Manger Object Type: Open Galactic Star Cluster Constellation: Cancer Right Ascension: 08 : 40.1 (h:m) Declination: +19 : 59 (deg:m) Distance: .577 (kly) Visual Brightness: 3.7 (mag) Apparent Dimension: 95.0 (arc min)
Let’s compare and contrast. Humans, on the one hand, have made enormous advances in science and technology, built cities, cars, computers, and phones. We have split the atom for war and for energy.
What has the Sun done? It’s a massive ball of plasma, made up of mostly hydrogen and helium. It just, kind of, sits there. Every now and then it burps up hydrogen gas into a coronal mass ejection. It’s not a stretch to say that the Sun, and all inanimate material in the Universe, isn’t the sharpest knife in the drawer.
And yet, the Sun has mastered a form of energy that we just can’t seem to wrap our minds around: fusion. It’s really infuriating, seeing the Sun, just sitting there, effortlessly doing something our finest minds have struggled with for half a century.
Why can’t we make fusion work? How long until we can finally catch up technologically with a sphere of ionized gas?
Our Sun in all its intense, energetic glory. Credit: NASA/SDO.
The trick to the Sun’s ability to generate power through nuclear fusion, of course, comes from its enormous mass. The Sun contains 1.989 x 10^30 kilograms of mostly hydrogen and helium, and this mass pushes inward, creating a core heated to 15 million degrees C, with 150 times the density of water.
It’s at this core that the Sun does its work, mashing atoms of hydrogen into helium. This process of fusion is an exothermic reaction, which means that every time a new atom of helium is created, photons in the form of gamma radiation are also released.
The only thing the Sun uses this energy for is light pressure, to counteract the gravity pulling everything inward. Its photons slowly make their way up through the Sun and then they’re released into space. So wasteful.
How can we replicate this on Earth?
Now gathering together a Sun’s mass of hydrogen here on Earth is one option, but it’s really impractical. Where would we put all that hydrogen. The better solution will be to use our technology to simulate the conditions at the core of the Sun.
If we can make a fusion reactor where the temperatures and pressures are high enough for atoms of hydrogen to merge into helium, we can harness those sweet sweet photons of gamma radiation.
Inside a Tokamak. Credit: Princeton Plasma Physics Laboratory
The main technology developed to do this is called a tokamak reactor; it’s a based on a Russian acronym for: “toroidal chamber with magnetic coils”, and the first prototypes were created in the 1960s. There are many different reactors in development, but the method is essentially the same.
A vacuum chamber is filled with hydrogen fuel. Then an enormous amount of electricity is run through the chamber, heating up the hydrogen into a plasma state. They might also use lasers and other methods to get the plasma up to 150 to 300 million degrees Celsius (10 to 20 times hotter than the Sun’s core).
Superconducting magnets surround the fusion chamber, containing the plasma and keeping it away from the chamber walls, which would melt otherwise.
Once the temperatures and pressures are high enough, atoms of hydrogen are crushed together into helium just like in the Sun. This releases photons which heat up the plasma, keeping the reaction going without any addition energy input.
Excess heat reaches the chamber walls, and can be extracted to do work.
The spherical tokamak MAST at the Culham Centre for Fusion Energy (UK). Photo: CCFE
The challenge has always been that heating up the chamber and constraining the plasma uses up more energy than gets produced in the reactor. We can make fusion work, we just haven’t been able to extract surplus energy from the system… yet.
Compared to other forms of energy production, fusion should be clean and safe. The fuel source is water, and the byproduct is helium (which the world is actually starting to run out of). If there’s a problem with the reactor, it would cool down and the fusion reaction would stop.
The high energy photons released in the fusion reaction will be a problem, however. They’ll stream into the surrounding fusion reactor and make the whole thing radioactive. The fusion chamber will be deadly for about 50 years, but its rapid half-life will make it as radioactive as coal ash after 500 years.
External view of Princeton’s Tokamak Fusion Test Reactor which operated from 1982 to 1997. Credit: Princeton Plasma Physics Laboratory (CC BY 3.0)
Now you know what fusion power is and how it works, what’s the current state, and how long until fusion plants give us unlimited cheap safe power, if ever?
Fusion experiments are measured by the amount of energy they produce compared to the amount of energy you put into them. For example, if a fusion plant required 100MW of electrical energy to produce 10 MW of output, it would have an energy ratio of 0.1. You want at least a ratio of 1. That means energy in equals energy out, and so far, no experiment has ever reached that ratio. But we’re close.
The EAST facility’s tokamak reactor, part of the Institute of Physical Science in Hefei. Credit: ipp.cas.cn
The Chinese are building the Experimental Advanced Superconducting Tokamak, or EAST. In 2016, engineers reported that they had run the facility for 102 seconds, achieving temperatures of 50 million C. If true, this is an enormous advancement, and puts China ahead in the race to create stable fusion. That said, this hasn’t been independently verified, and they only published a single scientific paper on the milestone.
Karlsruhe Institute of Technology’s Wendelstein 7-X (W7X) stellarator. Credit: Max-Planck-Institut für Plasmaphysik, Tino Schulz (CC BY-SA 3.0)
Researchers at the Karlsruhe Institute of Technology (KIT) in Germany recently announced that their Wendelstein 7-X (W7X) stellarator (I love that name), heated hydrogen gas to 80 million C for only a quarter of a second. Hot but short. A stellarator works differently than a tokamak. It uses twisted rings and external magnets to confine the plasma, so it’s good to know we have more options.
The biggest, most elaborate fusion experiment going on in the world right now is in Europe, at the French research center of Cadarache. It’s called ITER, which stands for the International Thermonuclear Experimental Reactor, and it hopes to cross that magic ratio.
The ITER Tokamak Fusion Reactor. Credits: ITER, Illus. T.Reyes
ITER is enormous, measuring 30 meters across and high. And its fusion chamber is so large that it should be able to create a self-sustaining fusion reaction. The energy released by the fusing hydrogen keeps the fuel hot enough to keep reacting. There will still be energy required to run the electric magnets that contain the plasma, but not to keep the plasma hot.
And if all goes well, ITER will have a ratio of 10. In other words, for every 10 MW of energy pumped in, it’ll generate 100 MW of usable power.
ITER is still under construction, and as of June 2015, the total construction costs had reached $14 billion. The facility is expected to be complete by 2021, and the first fusion tests will begin in 2025.
So, if ITER works as planned, we are now about 8 years away from positive energy output from fusion. Of course, ITER will just be an experiment, not an actual powerplant, so if it even works, an actual fusion-based energy grid will be decades after that.
At this point, I’d say we’re about a decade away from someone demonstrating that a self-sustaining fusion reaction that generates more power than it consumes is feasible. And then probably another 2 decades away from them supplying electricity to the power grid. By that point, our smug Sun will need to find a new job.
This illustration shows the final stages in the life of a supermassive star that fails to explode as a supernova, but instead implodes to form a black hole. Credit: NASA/ESA/P. Jeffries (STScI)
Collapsing stars are a rare thing to witness. And when astronomers are able to catch a star in the final phase of its evolution, it is a veritable feast for the senses. Ordinarily, this process consists of a star undergoing gravitational collapse after it has exhausted all of its fuel, and shedding its outer layers in a massive explosion (aka. a supernova). However, sometimes, stars can form black holes without the preceding massive explosion.
This process, what might be described as “going out not with a bang, but with a whimper”, is what a team of astronomers witnessed when observing N6946-BH1 – a star located in the Fireworks Galaxy (NGC 6946). Originally, astronomers thought that this star would exploded because of its significant mass. But instead, the star simply fizzled out, leaving behind a black hole.
The Fireworks Galaxy, a spiral galaxy located 22 million light-years from Earth, is so-named because supernova are known to be a frequent occurrence there. In fact, earlier this month, an amateur astronomer spotted what is now designated as SN 2017eaw. As such, three astronomers from Ohio Sate University (who are co-authors on the study) were expecting N6946-BH1 would go supernova when in 2009, it began to brighten.
Visible-light and near-infrared photos from NASA’s Hubble Space Telescope showing the giant star N6946-BH1 before and after it vanished out of sight by imploding to form a black hole. Credit: NASA/ESA/C. Kochanek (OSU)
However, by 2015, it appeared to have winked out. As such, the team went looking for the remnants of it with the help of colleagues from Ohio State University and the University of Oklahoma. Using the combined power of the Large Binocular Telescope (LBT) and NASA’s Hubble and Spitzer space telescopes, they realized that the star had completely disappeared from sight.
After it experienced a weak optical outburst in 2009, they had anticipated that this red supergiant would go supernova – which seemed logical given that it was 25 times as massive as our Sun. After winking out in 2015, they had expected to find that the star had merely dimmed, or that it had cast off a dusty shell of material that was obscuring its light from view.
Their efforts included an LBT survey for failed supernovae, which they combined with infrared spectra obtained by the Spitzer Space Telescope and optical data from Hubble. However, all the surveys turned up negative, which led them to only one possible conclusion: that N6946-BH1 must have failed to go supernova and instead went straight to forming a blackhole.
Simulated view of a black hole. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke, Radboud University
As Scott Adams – a former Ohio State student who is now an astrophysicist at the Cahill Center for Astrophysics (and the lead author of the study) – explained in a NASA press release:
“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae. This is just the fraction that would explain the very problem that motivated us to start the survey, that is, that there are fewer observed supernovae than should be occurring if all massive stars die that way.”
A major implication of this study is the way it could shed new light on the formation of very massive black holes. For some time now, astronomers have believed that in order to form a black hole at the end of its life cycle, a star would have to be massive enough to cause a supernova. But as the team observed, it doesn’t make sense that a star would blow off its outer layers and still have enough mass left over to form a massive black hole.
As Christopher Kochanek – a professor of astronomy at The Ohio State University, the Ohio Eminent Scholar in Observational Cosmology and a co-author of the team’s study – explained:
“The typical view is that a star can form a black hole only after it goes supernova. If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.”
This information is also important as far as the study of gravitational waves goes. In February of 2016, scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) announced the first detection of this strange phenomena, which were apparently generated by a massive black hole. If in fact massive black holes form from failed supernova, it would help astronomers to track down the sources more easily.
Be sure to check out this video of the observations made of this failed SN and black hole:
The southern constellation Columba. Credit: Torsten Bronger
Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the dove – the Columba constellation!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.
Since then, thanks to the efforts of astronomer and explorers, many more constellations have come to be recognized. One of these is the constellation Columba (also known as “the dove”), which was discovered in the 16th century. Located in the southern hemisphere, this small constellation is bordered by the constellations of Caelum, Canis Major, Lepus, Pictor, and Puppis.
Name and Meaning:
Since Columba was unknown to the ancient Greeks and Romans, no mythlogy is associated with it, but its original name was Columba Noachi, which refers to the Torah’s and Bible’s Dove of Noah that was the first bird to find land after the Deluge.
It could also belong to the story of Argo, where a dove was sent out to lead the Argonauts to safety between the clashing rocks. The legend of the dove is supported by the brightest star in the constellation – Alpha – whose name is Phact, Arabic for “ring dove”.
The constellation seen as “Columba Noachi” in Urania’s Mirror (1825). Credit: US Library of Congress/Wikipedia Commons
History of Observation:
Columba first appeared on the constellation charts of Petrus Plancius – a sixteen century Dutch astronomer and cartographer. In 1589, he created a celestial globe using what little information he could gather from the times explorers to help “fill in” the blank area around the south celestial pole.
Columba was then introduced into a large wall map of the constellations in 1592 and later included in Johann Bayer’s Uranometria sky atlas. In 1920, it was included among the 88 constellations recognized by the IAU, where it has remained to this day.
Notable Objects:
Columba has several major stars associated with it. The brightest is Alpha Columbae (aka. Phact), which is located approximately 270 light years from Earth. Phact is a double star that belongs to the spectral class B7IVe, and is omposed of a Be-type subgiant and a faint companion star. Its name is derived from the Arabic world Al-Fakhita, which means “the dove”.
Beta Columbae (aka. Wezn) is the second brightest star in the constellation, a giant K1-type star located 86 light years from Earth. It’s name is derived from the Arabic word Al-Wazen, which means “the weight”. Third is Delta Columbae (aka. Ghusn al Zaitun), a spectroscopic binary that is located approximately 237 light years away. Its name is derived from the Arabic phrase al-ghasn alzzaytun, which means “olive branch.”
The barred spiral galaxy NGC 1808. Credit: Jim Flood (Amateur Astronomers Inc., Sperry Observatory), Max Mutchler (STScI)
Columba is also home to several Deep Sky Objects. There’s NGC 1808, a barred spiral galaxy that is located approximately 40 million light years from Earth. Similar in many ways to the Milky Way, this galaxy has an unusual nuclear which is shaped like a warped disk and is believed to have a lot of star-forming activity within it.
There’s also NGC 1851 (aka. Caldwell 73), is a globular cluster located approximately 39,500 light years away, and NGC 1792, a starburst spiral galaxy that also goes by the name Bulliens Columbae (or the “bubbling galaxy”). This is due to its appearance, which is characterized by the patchy distribution of dust throughout the galaxy and the way this dust is heated by young stars.
Last, there’s ESO 306-17, a fossil group giant elliptical galaxy that is located at a distance of about 493 million light years from Earth. The galaxy spans about 1 million light years in diameter and is believed to have cannibalized smaller galaxies in its neighbourhood. Hence why it is designated as a fossil group, which refers to the fact that it is believed to be the end-result of a galaxy colliding and merging with a regular galaxy group.
Finding Columba:
Columba consists of 1 bright star and 5 primary stars, with 18 Bayer/Flamsteed designated stellar members. It is bordered by the constellations of Lepus, Caelum, Pictor, Puppis and Canis Major. Columba is easily visible to viewers at latitudes between +45° and -90° and is best seen at culmination during the month of February.
The globular cluster NGC 1851. Credit: NASA, JPL-Caltech, SSC
Get out your telescope and take a look at Alpha Columbae – the A symbol on the map. Here we have a a subgiant star – a star that has just stopped fusing hydrogen to helium – with an an apparent magnitude of approximately 2.6. Located about 268 light years from Earth, Phact is spinning rapidly… at a speed of at least 180 kilometers per second at its equator.
That’s over 90 times faster than our Sun! This rapid rotation causes Phact to flatten at its poles and to spin off a low density envelope about twice its radius. Now, look closely you’ll see that Phact is actually a binary star system. Its faint companion has an apparent magnitude of 12.3 and is 13.5″ distant from the main star.
Now aim binoculars at Beta Columbae – the B symbol on the map. Its proper name is Wazn the “Weight”. If you don’t think there is anything particularly interesting about this 86 light-year distant, spectral class K1IIICN+1, 3.12 magnitude star, then you better think again. This calm looking, core helium fusing giant star might be a little on the small side as giant stars go, but it is about 12 times the size of our own Sun and shines 53 times brighter.
Of course, that’s not all that unusual either. Nor is the fact that Wazn is about 2 billion years old. What is really strange is that Beta Columbae is scooting along through space at a speed of 103 kilometers per second. That’s about six to seven time faster than what’s considered “normal”! Why? It’s a runaway star, just like Mu Columbae.
Turn your binoculars toward the U symbol on the map and have a look. At 1,300 light years from our solar system, Mu is one of the few O-class stars that is visible to the unaided eye. Like Phact, Mu is a relatively fast rotating star that completes a full revolution approximately every 1.5 days.
Colour composite image of the starburst spiral galaxy NGC 1792. Credit: ESO
But Mu is also like Wazn – speeding along at relative velocity of over 200 km/s. Just where did these these two “runaways” come from? Chances are Wazn came from the other side of the Milky Way, while Mu may have originated from a binary star collision in Orion. Catch them while they’re still there!
Now aim your binoculars or telescopes at 7th magnitude globular cluster, NGC 1851 (RA 5 14 6.7 Dec -40 2 48). This Class II beauty was discovered by James Dunlop on May 29, 1826 and cataloged as Dunlop 508. What you’ll find is a very rich, almost impenetrable core surrounded by a nice halo of resolvable stars in a delightful field.
NGC 1851 has two distinct stellar populations with very different initial metal mixtures: a normal alpha-enhanced component, and one characterized by strong anti correlations among the CNONa abundances. Known in the Caldwell Catalog as Object 73, this fine object does well in all aperture sizes – even to Dunlop who almost 200 years ago wrote:
“An exceedingly bright, round, well-defined nebula, about 1.5′ diameter, exceedingly condensed, almost to the very margin. This is the brightest small nebula that I have seen. I tried several magnifying powers on this beautiful globe; a considerable portion round the margin is resolvable, but the compression to the centre is so great that I cannot reasonably expect to separate the stars. I compared this with the 68 Conn. des Temps, and this nebula greatly exceeds the 68 in condensation and brightness.”
Image of ESO 306-17, taken by the Advanced Camera for Surveys aboard the NASA/ESA Hubble Space Telescope. Credit: NASA/ESA/Michael West (ESO)
For a telescope challenge, try NGC 1792 (RA 05 05.2 Dec -37 59). Despite being billed at slightly fainter than magnitude 10, you’ll find the surface brightness of this spiral galaxy a little more in need of larger aperture. Noted as a starburst galaxy, NGC 1792 has a patchy distribution of dust throughout the galactic disc. The galaxy itself is abundant in neutral hydrogen gas and is in the star formation process.
The galaxy is characterized by unusually luminous far-infrared radiation from the young stars heating the dust with their intense activity. This activity could be caused by gravitational interaction with galaxy NGC 1808 (RA 5 7 42.3 Dec -37 30 47) – also a Seyfert galaxy. Easily seen in larger telescopes as an elongated glow, with a bright, round central core. There’s a reason for that…
The barred spiral galaxy NGC 1808 is undergoing an episode of intense star formation near its very center, perhaps triggered by rotation of the bar or by material transported inward along the bar. This new star formation is somehow being organized into clusters of between 10 and 100 light years in diameter, and filaments of dark, obscuring dust are mixed in with the gas and stars.
Thanks to studies done with the XMM-Newton and Chandra observatories, they have directly proved the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). What a show!
Now try your luck with galactic star cluster NGC 1963 (RA 05 32.2 Dec -36 23). While it is not a very rich and populous star cluster, it is an interesting stellar association of perhaps two dozen stars arranged in chains over a wide field with a size of 10.0′. Look for an asterism that appears like the number 3!
Freeze-dried mice sperm that spent nine months in space aboard the iSS were sucessfully used to create healthy offspring. Credit: Sayaka Wakayama/University of Yamanashi via AP
With proposed missions to Mars and plans to establish outposts on the Moon in the coming decades, there are several questions about what effects time spent in space or on other planets could have on the human body. Beyond the normal range of questions concerning the effects of radiation and lower-g on our muscles, bones, and organs, there is also the question of how space travel could impact our ability to reproduce.
Earlier this week – on Monday, May 22nd – a team of Japanese researchers announced findings that could shed light on this question. Using a sample of freeze-dried mouse sperm, the team was able to produce a litter of healthy baby mice. As part of a fertility study, the mouse sperm had spent nine months aboard the International Space Station (between 2013 and 2014). The real question now is, can the same be done for human babies?
The study was led by Sayaka Wakayama, a student researcher at the University of Yamanashi‘s Advanced Biotechnology Center. As she and her colleagues explain in their study – which was recently published in the Proceedings of the National Academy of Sciences – assisted reproductive technology will be needed if humanity ever intends to live in space long-term.
The International Space Station (ISS), seen here with Earth as a backdrop. Credit: NASA
As such, studies that address the effect that living in space could have on human reproduction are needed first. These need to address the impact microgravity (or low-gravity) could have on fertility, human abilities to conceive, and the development of children. And more importantly, they need to deal with one of the greatest hazards of spending time in space – which is the threat posed by solar and cosmic radiation.
To be fair, one need not go far to feel the effects of space radiation. The ISS regularly receives more than 100 times the amount of radiation that Earth’s surface does, which can result in genetic damage if sufficient safeguards are not in place. On other Solar bodies – like Mars and the Moon, which do not have a protective magnetosphere – the situation is similar.
And while the effects of radiation on adults has been studied extensively, the potential damage that could be caused to our offspring has not. How might solar and cosmic radiation affect our ability to reproduce, and how might this radiation affect children when they are still in the womb, and once they are born? Hoping to take the first steps in addressing these questions, Wakayama and her colleagues selected the spermatozoa of mice.
They specifically chose mice since they are a mammalian species that reproduces sexually. As Sayaka Wakayama explained Universe Today via email:
“So far, only fish or salamanders were examined for reproduction in space. However, mammalian species are very different compared to those species, such as being born from a mother (viviparity). To know whether mammalian reproduction is possible or not, we must use mammalian species for experiments. However, mammalian species such as mice or rats are very sensitive and difficult to take care of by astronauts aboard the ISS, especially for a reproduction study. Therefore, we [have not conducted these studies] until now. We are planning to do more experiments such as the effect of microgravity for embryo development.”
Human sperm stained for semen quality testing in the clinical laboratory. Credit: Bobjgalindo/Wikipedia Commons
The samples spent nine months aboard the ISS, during which time they were kept at a constant temperature of -95 °C (-139 °F). During launch and recovery, however, they were at room temperature. After retrieval, Wakayama and her team found that the samples had suffered some minor damage,.
“Sperm preserved in space had DNA damage even after only 9 months by space radiation,” said Wakayama. “However, that damage was not strong and could be repaired when fertilized by oocytes capacity. Therefore, we could obtain normal, healthy offspring. This suggests to me that we must examine the effect when sperm are preserved for longer periods.”
In addition to being reparable, the sperm samples were still able to fertilize mouse embryos (once they were brought back to Earth) and produce mouse offspring, all of which grew to maturity and showed normal fertility levels. They also noted that the fertilization and birth rates were similar to those of control groups, and that only minor genomic differences existed between those and the mouse created using the test sperm.
From all this, they demonstrated that while exposure to space radiation can damage DNA, it need not affect the production of viable offspring (at least within a nine month period). Moreover, the results indicate that human and domestic animals could be produced from space-preserved spermatozoa, which could be mighty useful when it comes to colonizing space and other planets.
A Pacific pocket mouse pup and its mother appear outside their artificial burrow at the San Diego Zoo. Credit: Ken Bohn/San Diego Zoo/AP
As Wakayama put it, this research builds on fertilization practices already established on Earth, and demonstrated that these same practices could be used in space:
“Our main subject is domestic animal reproduction. In the current situation on the ground, many animals are born from preserves spermatozoa. Especially in Japan, 100% of milk cows were born from preserved sperm due to economic and breeding reasons. Sometimes, sperm that has been stored for more than 10 years was used to produce cows. If humans live in space for many years, then, our results showed that we can eat beefsteak in the space. For that purpose, we did this study. For humans, our finding will probably help infertile couples.”
This research also paves the way for additional tests that would seek to measure the effects of space radiation on ova and the female reproduction system. Not only could these tests tell us a great deal about how time in space could affect female fertility, it could also have serious implications for astronaut safety. As Ulrike Luderer, a professor of medicine at the University of California and one of the co-authors on the paper said in a statement to the AFP:
“These types of exposures can cause early ovarian failure and ovarian cancer, as well as other osteoporosis, cardiovascular disease and neurocognitive diseases like Alzheimer’s. Half the astronauts in the NASA’s new astronaut classes are women. So it is really important to know what chronic health effects there could be for women exposed to long-term deep space radiation.”
Future space colonies could rely on frozen sperm and ova to produce livestock, and maybe even humans. Credit: Rick Guidice/NASA Ames Research Center
However, a lingering issue with these sorts of tests is being able to differentiate between the effects of microgravity and radiation. In the past, research has been conducted that showed how exposure to simulated microgravity can reduce DNA repair capacity and induce DNA damage in humans. Other studies have raised the issue of the interplay between the two, and how further experiments are needed to address the precise impact of each.
In the future, it may be possible to differentiate between the two by placing samples of spermatazoa and ova in a torus that is capable of simulating Earth gravity (1 g). Similarly, shielded modules could be used to isolate the effects of low or even micro-gravity. Beyond that, there will likely be lingering uncertainties until such time as babies are actually born in space, or in a lunar or Martian environment.
And of course, the long-terms impact of reduced gravity and radiation on human evolution remains to be seen. In all likelihood, that won’t become clear for generations to come, and will require multi-generational studies of children born away from Earth to see how they and their progeny differ.
Artist's concept of KIC 8462852, which has experienced unusual changes in luminosity over the past few years. Credit: NASA, JPL-Caltech
KIC 8462852 (aka. Tabby’s Star) captured the world’s attention back in September of 2015 when it was found to be experiencing a mysterious drop in brightness. A week ago (on May 18th), it was announced that the star was at it again, which prompted observatories from all around the world to train their telescopes on the star so they could observe the dimming as it happened.
The interior structure of Neptune. Credit: Moscow Institute of Physics and Technology
Since it’s discovery in the mid-19th century, Neptune has consistently been a planet of mystery. As the farthest planet from our Sun, it has only been visited by a single robotic mission. And there are still many unanswered questions about what kind of mechanics power its interior. Nevertheless, what we have learned about the planet in the course of the past few decades is considerable.
For example, thanks to the Voyager 2 probe and multiple surveys using Earth-based instruments, scientists have managed to gain a pretty good understanding of Neptune’s structure and composition. In addition to knowing what makes up its atmosphere, planetary models have also predicted what the interior of the planet looks like. So just what is Neptune made of?
Structure and Composition:
Neptune, like the rest of the gas giant planets in the Solar System, can be broken up into various layers. The composition of Neptune changes depending on which of these layers you’re looking at. The outermost layer of Neptune is the atmosphere, forming about 5-10% of the planet’s mass, and extending up to 20% of the way down to its core.
Composition and interior structure of Neptune. Credit: NASA
Beneath the atmosphere is the planet’s large mantle. This is a superheated liquid region where temperatures can reach as high as 2,000 to 5,000 K (1727 – 4727 °C; 3140 – 8540 °F). The mantle is equivalent to 10 – 15 Earth masses and is rich in water, ammonia and methane. This mixture is referred to as icy even though it is a hot, dense fluid, and is sometimes called a “water-ammonia ocean”.
Increasing concentrations of methane, ammonia and water are found in the lower regions of the atmosphere. Unlike Uranus, Neptune’s composition has a higher volume of ocean, whereas Uranus has a smaller mantle. Like the other gas/ice giants, Neptune is believed to have a solid core, the composition of which is still subject to guesswork. However, the theory that it is rocky and metal-rich is consistent with current theories of planet formation.
In accordance with these theories, the core of Neptune is composed of iron, nickel and silicates, with an interior model giving it a mass about 1.2 times that of Earth. The pressure at the center is estimated to be 7 Mbar (700 GPa), about twice as high as that at the center of Earth, and with temperatures as high as 5,400 K. At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that rain downwards like hailstones.
Due to its smaller size and higher concentrations of volatiles relative to Jupiter and Saturn, Neptune (much like Uranus) is often referred to as an “ice giant” – a subclass of a giant planet. Also like Uranus, Neptune’s internal structure is differentiated between a rocky core consisting of silicates and metals; a mantle consisting of water, ammonia and methane ices; and an atmosphere consisting of hydrogen, helium and methane gas.
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
Neptune’s Atmosphere:
Neptune’s atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the way towards the core, where it reaches pressures of about 10 GPa – or about 100,000 times that of Earth’s atmosphere. At high altitudes, Neptune’s atmosphere is 80% hydrogen and 19% helium, with a trace amount of methane.
As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune’s is darker and more vivid. Because Neptune’s atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune’s more intense coloring.
Neptune’s atmosphere is subdivided into two main regions: the lower troposphere (where temperature decreases with altitude), and the stratosphere (where temperature increases with altitude). The boundary between the two, the tropopause, lies at a pressure of 0.1 bars (10 kPa). The stratosphere then gives way to the thermosphere at a pressure lower than 10-5 to 10-4 microbars (1 to 10 Pa), which gradually transitions to the exosphere.
Neptune’s spectra suggest that its lower stratosphere is hazy due to condensation of products caused by the interaction of ultraviolet radiation and methane (i.e. photolysis), which produces compounds such as ethane and ethyne. The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide, which are responsible for Neptune’s stratosphere being warmer than that of Uranus.
Color and contrast-modified image that emphasizes Neptune’s atmospheric features. Neptune’s Great Dark Spot stands out as the most prominent feature on the left. Credit: Erich Karkoschka
For reasons that remain obscure, the planet’s thermosphere experiences unusually high temperatures of about 750 K (476.85 °C/890 °F). The planet is too far from the Sun for this heat to be generated by ultraviolet radiation, which means another heating mechanism is involved – which could be the atmosphere’s interaction with ion’s in the planet’s magnetic field, or gravity waves from the planet’s interior that dissipate in the atmosphere.
Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours, which is slower than the 16.1-hour rotation of the planet’s magnetic field. By contrast, the reverse is true for the polar regions where the rotation period is 12 hours.
This differential rotation is the most pronounced of any planet in the Solar System, and results in strong latitudinal wind shear and violent storms. The three most impressive were all spotted in 1989 by the Voyager 2 space probe, and then named based on their appearances.
The first to be spotted was a massive anticyclonic storm measuring 13,000 x 6,600 km and resembling the Great Red Spot of Jupiter. Known as the Great Dark Spot, this storm was not spotted five later (Nov. 2nd, 1994) when the Hubble Space Telescope looked for it. Instead, a new storm that was very similar in appearance was found in the planet’s northern hemisphere, suggesting that these storms have a shorter life span than Jupiter’s.
Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
The Scooter is another storm, a white cloud group located farther south than the Great Dark Spot. This nickname first arose during the months leading up to the Voyager 2 encounter in 1989, when the cloud group was observed moving at speeds faster than the Great Dark Spot.
The Small Dark Spot, a southern cyclonic storm, was the second-most-intense storm observed during the 1989 encounter. It was initially completely dark; but as Voyager 2 approached the planet, a bright core developed and could be seen in most of the highest-resolution images.
Exploration:
The Voyager 2 probe is the only spacecraft to have ever visited Neptune. The spacecraft’s closest approach to the planet occurred on August 25th, 1989, which took place at a distance of 4,800 km (3,000 miles) above Neptune’s north pole. Because this was the last major planet the spacecraft could visit, it was decided to make a close flyby of the moon Triton – similar to what had been done for Voyager 1‘s encounter with Saturn and its moon Titan.
The spacecraft performed a near-encounter with the moon Nereid before it came to within 4,400 km of Neptune’s atmosphere on August 25th, then passed close to the planet’s largest moon Triton later the same day. The spacecraft verified the existence of a magnetic field surrounding the planet and discovered that the field was offset from the center and tilted in a manner similar to the field around Uranus.
Neptune’s rotation period was determined using measurements of radio emissions and Voyager 2 also showed that Neptune had a surprisingly active weather system. Six new moons were discovered during the flyby, and the planet was shown to have more than one ring.
While no missions to Neptune are currently being planned, some hypothetical missions have been suggested. For instance, a possible Flagship Mission has been envisioned by NASA to take place sometime during the late 2020s or early 2030s. Other proposals include a possible Cassini-Huygens-style “Neptune Orbiter with Probes”, which was suggested back in 2003.
Another, more recent proposal by NASA was for Argo – a flyby spacecraft that would be launched in 2019, which would visit Jupiter, Saturn, Neptune, and a Kuiper belt object. The focus would be on Neptune and its largest moon Triton, which would be investigated around 2029.
Given its distance from Earth, it is no secret why the Trans-Neptunian region remains mysterious to us. In the coming decades, several proposed missions are expected to travel there and explore its rich population of icy bodies and the giant planet for which it is named. From these studies, we are likely to learn a great deal about Neptune and the history of the Solar System.
