New Horizons Spots Neptune’s Moon Triton


New Horizons got a great shot of Neptune’s moon Triton last fall, as it was trucking toward Pluto and the Kuiper Belt. 

The mission was 2.33 billion miles (3.75 billion kilometers) from Neptune on Oct. 16, when its Long Range Reconnaissance Imager (LORRI) locked onto the planet and snapped away. The craft was following a programmed sequence of commands as part of its annual checkout. NASA released the image Thursday afternoon.

Mission scientists say the shot was good practice for imaging Pluto, which New Horizons will do in 2015. Neptune’s moon Triton and Pluto — the former planet retitled in 2006 as the ambassador to the Kuiper Belt — have much in common.

“Among the objects visited by spacecraft so far, Triton is by far the best analog of Pluto,” said New Horizons Principal Investigator Alan Stern. 

Triton is only slightly larger than Pluto, boasting a 1,700-mile (2,700-kilometers) diameter compared to Pluto’s 1,500-mile (2,400-kilometer) girth. Both objects have atmospheres primarily composed of nitrogen gas with a surface pressure only 1/70,000th of Earth’s, and comparably cold surface temperatures. Temperatures average -390 degrees F (-199 degrees C) on Triton and -370 degrees F (-188 degrees C) on Pluto. 

Triton is widely believed to have once been a member of the Kuiper Belt that was captured into orbit around Neptune, probably during a collision early in the solar system’s history. Pluto was the first Kuiper Belt object to be discovered.

Furthermore, “We wanted to test LORRI’s ability to measure a faint object near a much brighter one using a special tracking mode,” said New Horizons Project Scientist Hal Weaver, of Johns Hopkins University, “and the Neptune-Triton pair perfectly fit the bill.”

LORRI was operated in 4-by-4 format (the original pixels are binned in groups of 16), and the spacecraft was put into a special tracking mode to allow for longer exposure times to maximize its sensitivity.

Mission scientists also wanted to measure Triton itself, to follow up on observations made by the Voyager 2 spacecraft during its flyby of Neptune in 1989. Those images revealed evidence of cryovolcanic activity and cantaloupe-like terrain. New Horizons can observe Neptune and Triton at solar phase angles (the Sun-object-spacecraft angle) that are not possible to achieve from Earth-based facilities, yielding new insight into the properties of Titan’s surface and Neptune’s atmosphere.

New Horizons is currently in electronic hibernation, 1.2 billion miles (1.93 billion kilometers) from home, speeding away from the Sun at 38,520 miles (61,991 kilometers) per hour. LORRI will continue to observe the Neptune-Triton pair during annual checkouts until the Pluto encounter in 2015. 

LEAD IMAGE CAPTION: The top frame is a composite, full-frame (0.29° by  0.29°) LORRI image of Neptune taken Oct. 16, 2008, using an exposure time of 10 seconds and 4-by-4 pixel re-binning to achieve its highest possible sensitivity. The bottom frame is a twice-magnified view that more clearly shows the detection of Triton, Neptune’s largest moon. Neptune is the brightest object in the field and is saturated (on purpose) in this long exposure. Triton, which is about 16 arcsec east (celestial north is up, east is to the left) of Neptune, is approximately 180 times fainter.  All the other objects in the image are background field stars. The dark “tails” on the brightest objects are artifacts of the LORRI charge-coupled device (CCD); the effect is small but easily seen in this logarithmic intensity stretch. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

Source: NASA

Pluto Spacecraft Gets Brain Transplant

Artist rendition of New Horizons in the Kuiper Belt. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)


Still seven years away from its rendezvous with Pluto, the New Horizons spacecraft was awoken from hibernation for the second annual checkout of all systems. The spacecraft and its team back on Earth will also undergo three months of operations as the New Horizons will make observations of Uranus, Neptune, and Pluto. But the first order of business was uploading an upgraded version of the software that runs the spacecraft’s Command and Data Handling system. “Our ‘brain transplant’ was a success,” says New Horizons Principal Investigator Alan Stern. “The new software – which guides how New Horizons carries out commands and collects and stores data – is now on the spacecraft’s main computer and operating, over a billion miles from home!”

The mission ops team at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, radioed the software load and the commands to start it earlier this week through NASA’s Deep Space Network of antennas to the spacecraft, now just more than 1.01 billion miles (1.62 billion kilometers) from Earth. In the next 10 days the team will beam up additional new software for both the spacecraft’s Autonomy and Guidance and Control systems.

Space Science Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
Space Science Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Alice Bowman, New Horizons mission operations manager at APL, says the spacecraft and its computers are healthy. “The new software fixes a few bugs and enhances the way these systems operate, based on what we’ve learned in running the spacecraft in the nearly three years since launch,” she says. “They also configure the onboard systems to be ready to support the Pluto-Charon encounter rehearsals scheduled for next summer.”

New Horizons is more than 200 million miles beyond Saturn’s orbit and more than 11 astronomical units (1.02 billion miles) from the Sun, flying about a million miles per day toward Pluto. Annual Checkout 2 (ACO-2) continues through mid-December; follow its progress through frequent updates on the New Horizons Twitter page.

Source: New Horizons Press Release

How Old is Triton’s Surface?


With all of the press going to the moons of Jupiter and Saturn, it’s about time that Neptune got a turn. Triton, one of the moons of Neptune, is curious, with large swaths of the planet resembling the skin of a cantaloupe and a retrograde orbit (opposite that of Neptune’s rotation). Its surface is thought to be rather young, and a new method of counting the craters that pock the moon may push the age of Triton’s surface back even younger than previously thought.

Dr. Paul Schenk of the Lunar and Planetary Institute in Houston, and Kevin Zahnle of the NASA Ames Research Center in California revisited the pictures of Triton’s surface that the Voyager 2 spacecraft took in 1989. By clarifying the images with current technology, they were able to count with very high accuracy the amount of craters, and determine the possible causes of the craters. Their results were published in the July 2007 issue of the journal Icarus, in a paper titled On the negligible age of the surface of Triton.

“Our new crater counts benefit from several improvements in the quality of the Voyager images. Although this does not make invisible craters visible, it does increase the ability to discriminate impact features on Triton,” the researchers wrote.

The images showed that the leading hemisphere — the hemisphere of the planet in the direction of its orbit around Neptune — contains many more craters than that of the trailing hemisphere. Triton is tidally locked to Neptune, which means that – like our Moon – an observer on Neptune would always see the same face of Triton. Thus, the same hemisphere would always face the direction of Triton’s orbit around Neptune.

The researchers propose, “Our map of craters on Triton indicates that all definitive impact craters are on the leading hemisphere. The apparent cratering asymmetry of Triton is extreme. The absence of craters on the trailing hemisphere, and the low frequency of craters near the boundary between leading and trailing hemispheres is unique in the Solar System.”

Since Triton is rotating in the opposite direction of everything else that goes around Neptune, it acts like a giant “vacuum cleaner,” and picks up any debris orbiting the planet in a prograde (the same as Neptune’s rotation) direction.

Triton is thought to have given itself a makeover very recently because it was captured by Neptune long ago; most likely, Triton was one body in a binary system, and when Neptune captured it, the other body was thrown out of the Solar System. After being captured, all of the energy that went into slowing Triton down into orbit around Neptune was transferred into heat that melted the surface and interior of the planet. This heat could have lasted for millions of years, and the tidal energy from Neptune may still warm the interior of Triton today.

Normally, areas that have less craters have been resurfaced more recently, and thus are generally younger than surfaces with lots of craters. By analyzing the density of the craters, and using information about the type and frequency of debris that possibly caused them, the researchers were able to calculate that the terrain on the trailing hemisphere with less craters than that of the leading hemisphere was actually older than the area with more craters.

“Whatever their origin, the paucity of impact craters (and heliocentric craters in particular) suggests that Triton’s surface is very young, younger than 100 million years and possibly as young as a few million years. A return to Neptune and its vigorous, dynamic moon Triton is long overdue,” the researchers wrote.

Source: Icarus

Podcast: Neptune


We’ve reached Neptune, the final planet in our tour through the solar system – but don’t worry! The tour’s not over, but after this week we’ll be all out of planets. Neptune has a controversial story about its discovery, some of the strongest winds in the solar system and some weird moons.
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Neptune – Show notes and transcript

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Neptune’s South Pole is the Warmest Place on the Planet


Here on Earth we think of the poles as cold places, but on Neptune, it’s just the opposite. New images of the planet’s southern pole show that it’s actually 10-degrees warmer than the rest of Neptune. Now don’t pack your bathing suit just yet, Neptune’s average temperature is still -200 degrees Celsius (-328 F); so it’s still really, really cold.

The images were gathered using the European Southern Observatory’s Very Large Telescope (now that’s how you name a telescope). The observatory uses a special mid-infrared camera/spectrometer to reveal the different temperatures across planet.

Obviously Neptune is different from the Earth, but consider this. The planet is located 30 times farther away from the Sun than the Earth. This means only 1/900th the sunlight reaches Neptune than what we get here on Earth. Still, it’s enough sunlight to warm up the southern pole, which is currently tilted towards the Sun.

It’s been receiving the warmth from the Sun for about 40 years now, and the ongoing input of solar energy continuously heats up the polar region to the point that it’s warmer than any other part of Neptune by about 10 degrees Celsius. This heating also whips up the planets winds into some of the strongest in the Solar System. On Neptune, winds can travel more than 2,000 km/hour, faster than any other planet – you definitely don’t want to bring your swimsuit.

The temperatures in the region are high enough that methane gas, normally frozen out of the upper atmosphere, can actually leak out through the region. And this helps explain why scientists have seen abundances of this molecule in the atmosphere.

Original Source: ESO News Release

Are There Oceans on Neptune?

Are There Oceans on Neptune
Smaller and cooler than the gas giants, Neptune and Uranus are classified as ice giants. It’s a good name, since they do have large quantities of water ice mixed in with a largely hydrogen and helium atmosphere. There’s very little water at the cloud tops, but the percentage of water increases as you descend towards the heavier core. Could there be a layer on Neptune with enough pressure and temperature for liquid water to form into vast oceans? And if not Neptune, what about a Neptune-like planet orbiting another star?
Continue reading “Are There Oceans on Neptune?”

Three Trojans Found in Neptune’s Orbit

Researchers have discovered three new objects sharing trailing behind Neptune in the same orbit. These asteroid-sized objects are locked into stable positions – called Lagrange points – through their interaction with Neptune’s gravity; Jupiter has over 1800 Trojans of its own. Astronomers had already discovered one Trojan for Neptune, so this raises its total to 4. The discovery was made using the Carnegie 6.5 Magellan Telescopes in Chile and the 8-meter Gemini North telescope on Mauna Kea, Hawaii.
Continue reading “Three Trojans Found in Neptune’s Orbit”

Three Neptunes Orbiting Another Star

An artist’s impression of a planetary system around HD 69830. Image credit: ESO. Click to enlarge
Astronomers have discovered a nearby star that’s home to three Neptune-sized planets; no super-Jupiters here. The star, HD 69830, is located 41 light-years away in the constellation of Puppis. With magnitude 5.95, it’s just possible to see with the unaided eye. The discovery was made using the European Southern Observatory’s 3.6 metre telescope at La Silla in Chile. The planets orbit their star in 8.67, 31.6 and 197 days respectively.

Using the ultra-precise HARPS spectrograph on ESO’s 3.6-m telescope at La Silla (Chile), a team of European astronomers have discovered that a nearby star is host to three Neptune-mass planets. The innermost planet is most probably rocky, while the outermost is the first known Neptune-mass planet to reside in the habitable zone. This unique system is likely further enriched by an asteroid belt.

“For the first time, we have discovered a planetary system composed of several Neptune-mass planets”, said Christophe Lovis, from the Geneva Observatory and lead-author of the paper presenting the results.

During more than two years, the astronomers carefully studied HD 69830, a rather inconspicuous nearby star slightly less massive than the Sun. Located 41 light-years away towards the constellation of Puppis (the Stern), it is, with a visual magnitude of 5.95, just visible with the unaided eye. The astronomers’ precise radial-velocity measurements allowed them to discover the presence of three tiny companions orbiting their parent star in 8.67, 31.6 and 197 days.

“Only ESO’s HARPS instrument installed at the La Silla Observatory, Chile, made it possible to uncover these planets”, said Michel Mayor, also from Geneva Observatory, and HARPS Principal Investigator. “Without any doubt, it is presently the world’s most precise planet-hunting machine”.

The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That’s the speed of a person walking briskly. Such tiny signals could not have been distinguished from ‘simple noise’ by most of today’s available spectrographs.

The newly found planets have minimum masses between 10 and 18 times the mass of the Earth. Extensive theoretical simulations favour an essentially rocky composition for the inner planet, and a rocky/gas structure for the middle one. The outer planet has probably accreted some ice during its formation, and is likely to be made of a rocky/icy core surrounded by a quite massive envelope. Further calculations have also shown that the system is in a dynamically stable configuration.

The outer planet also appears to be located near the inner edge of the habitable zone, where liquid water can exist at the surface of rocky/icy bodies. Although this planet is probably not Earth-like due to its heavy mass, its discovery opens the way to exciting perspectives.

“This alone makes this system already exceptional”, said Willy Benz, from Bern University, and co-author. “But the recent discovery by the Spitzer Space Telescope that the star most likely hosts an asteroid belt is adding the cherry to the cake.”

With three roughly equal-mass planets, one being in the habitable zone, and an asteroid belt, this planetary system shares many properties with our own solar system.

“The planetary system around HD 69830 clearly represents a Rosetta stone in our understanding of how planets form”, said Michel Mayor. “No doubt it will help us better understand the huge diversity we have observed since the first extra-solar planet was found 11 years ago.”

Original Source: ESO News Release

Neptune Kidnapped Triton from Another Planet

Neptune’s largest moon, Triton. Image credit: NASA. Click to enlarge
Neptune’s moon Triton is unique in the Solar System because it’s the only large moon that orbits in the opposite direction to its planet’s rotation. Researchers have developed a computer model that explains how Neptune could have captured Triton from another planet during a close approach. Under this scenario, Triton was originally part of a binary system with another planet. They got too close to Neptune and Triton was torn away.

Neptune’s large moon Triton may have abandoned an earlier partner to arrive in its unusual orbit around Neptune. Triton is unique among all the large moons in the solar system because it orbits Neptune in a direction opposite to the planet’s rotation (a “retrograde” orbit). It is unlikely to have formed in this configuration and was probably captured from elsewhere.

In the May 11 issue of the journal Nature, planetary scientists Craig Agnor of the University of California, Santa Cruz, and Douglas Hamilton of the University of Maryland describe a new model for the capture of planetary satellites involving a three-body gravitational encounter between a binary and a planet. According to this scenario, Triton was originally a member of a binary pair of objects orbiting the Sun. Gravitational interactions during a close approach to Neptune then pulled Triton away from its binary companion to become a satellite of Neptune.

“We’ve found a likely solution to the long-standing problem of how Triton arrived in its peculiar orbit. In addition, this mechanism introduces a new pathway for the capture of satellites by planets that may be relevant to other objects in the solar system,” said Agnor, a researcher in UCSC’s Center for the Origin, Dynamics, and Evolution of Planets.

With properties similar to the planet Pluto and about 40 percent more massive, Triton has an inclined, circular orbit that lies between a group of small inner moons with prograde orbits and an outer group of small satellites with both prograde and retrograde orbits. There are other retrograde moons in the solar system, including the small outer moons of Jupiter and Saturn, but all are tiny compared to Triton (less than a few thousandths of its mass) and have much larger and more eccentric orbits about their parent planets.

Triton may have come from a binary very similar to Pluto and its moon Charon, Agnor said. Charon is relatively massive, about one-eighth the mass of Pluto, he explained.

“It’s not so much that Charon orbits Pluto, but rather both move around their mutual center of mass, which lies between the two objects,” Agnor said.

In a close encounter with a giant planet like Neptune, such a system can be pulled apart by the planet’s gravitational forces. The orbital motion of the binary usually causes one member to move more slowly than the other. Disruption of the binary leaves each object with residual motions that can result in a permanent change of orbital companions. This mechanism, known as an exchange reaction, could have delivered Triton to any of a variety of different orbits around Neptune, Agnor said.

An earlier scenario proposed for Triton is that it may have collided with another satellite near Neptune. But this mechanism requires the object involved in the collision to be large enough to slow Triton down, but small enough not to destroy it. The probability of such a collision is extremely small, Agnor said.

Another suggestion was that aerodynamic drag from a disk of gas around Neptune slowed Triton down enough for it to be captured. But this scenario puts constraints on the timing of the capture event, which would have to occur early in Neptune’s history when the planet was surrounded by a gas disk, but late enough that the gas would disperse before it slowed Triton’s orbit enough to send the moon crashing into the planet.

In the past decade, many binaries have been discovered in the Kuiper belt and elsewhere in the solar system. Recent surveys indicate that about 11 percent of Kuiper belt objects are binaries, as are about 16 percent of near-Earth asteroids.

“These discoveries pointed the way to our new explanation of Triton’s capture,” Hamilton said. “Binaries appear to be a ubiquitous feature of small-body populations.”

The binary Pluto and its moon Charon and the other binaries in the Kuiper belt are especially relevant for Triton, as their orbits abut Neptune’s, he said.

“Similar objects have probably been around for billions of years, and their prevalence indicates that the binary-planet encounter that we propose for Triton’s capture is not particularly restrictive,” Hamilton said.

The exchange reaction described by Agnor and Hamilton may have broad applications in understanding the evolution of the solar system, which contains many irregular satellites. The researchers plan to explore the implications of their findings for other satellite systems.

This research was supported by grants from NASA’s Planetary Geology and Geophysics, Outer Planet Research, and Origins of Solar Systems programs.

Original Source: UC Santa Cruz

Hubble’s Neptune Movies

Blue-green Neptune and its satellites. Image credit: NASA/ESA Click to enlarge
New NASA Hubble Space Telescope images of the distant planet Neptune show a dynamic atmosphere and capture the fleeting orbits of its satellites. The images have been assembled into a time-lapse movie revealing the orbital motion of the satellites.

Images were taken in 14 different colored filters probing various altitudes in Neptune’s deep atmosphere so that scientists can study the haze and clouds in detail.

These are several snapshots from the Neptune movie.

The natural-color view of Neptune (to left), common to naked eye telescopic views by amateur astronomers, reveals a cyan colored planet. Methane gas in Neptune’s atmosphere absorbs most of the red sunlight hitting the planet, making it look blue-green. The image was created by combining images in red, green, and blue light.

Neptune’s subtle features are more visible in the enhanced-color view (top right). Images taken in special methane filters show details not visible to the human eye (bottom right). The features seen in this enhanced image must be above most of the sunlight-absorbing methane to be detectable through these special filters.

The planet is so dark at the methane wavelengths that long exposures can be taken, revealing some of Neptune’s smaller moons. Clockwise from the top (in composite image at left), these moons are Proteus (the brightest), Larissa, Despina, and Galatea. Neptune had 13 moons at last count.

Neptune is the most distant giant planet in our Solar System, orbiting the Sun every 165 years. It is so large tht nearly 60 Earths could fit inside it. A day on Neptune is between 14 hours and 19 hours. The inner two thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is a mixture of heated gases comprised of hydrogen, helium, water and methane.

On April 29 and 30, 2005, Hubble images were taken every 4-5 hours, spaced at about a quarter of Neptune’s rotational period. These where combined to create a time-lapse movie of the dynamic planet.

Original Source: Hubble News Release