Has Voyager 1 finally left the Solar System?

An answer to this question has been proclaimed so many times in the last few years that it has almost lost its effect. Part of the confusion lies in how we define “solar system.” Is it the edge of planetary orbits or the end of the Sun’s influence…or is there yet another definition?

Launched in 1977, the craft has been hurtling through space at an incredible 38,000 miles per hour, sprinting nearly 1,000,000 miles per day. It passed the orbit of the farthest planet Neptune on August 25, 1989 (at the time, due to its highly elliptical orbit, the then-planet Pluto was closer to the Sun than Neptune). Its twin spacecraft, Voyager 2, actually flew close to the planet itself. In 1990, with their planetary missions accomplished, both Voyager missions were renamed the Voyager Interstellar Mission. This consists of three phases: detection of the termination shock (the edge of the Sun’s magnetic influence, where the solar wind slows); exploration of the heliopause (the interface between the solar wind and the interstellar wind); and exploration of interstellar space (the region where the interstellar wind dominates). In December 2004, Voyager crossed the termination shock. Roughly ten years later, the craft was expected to transverse the heliopause, which many consider the edge of the Solar System.

And on August 25, 2012, 35 years after its launch and 12 billion miles (125.3 AU) from the Sun, Voyager 1 officially crossed into interstellar space.

The determination that the event actually occurred, however, did not come until last week. What took so long?

The Sun ejects plasma material (called the “solar wind”) out into a bubble called the heliosphere. The plasma outside that sphere comes from stellar explosions millions of years ago and has since been dispersed throughout the galaxy. The interaction between the heliosphere and plasma is the boundary between the two.

Voyager was looking to detect that boundary between plasmas; however, it could not do this directly because the plasma detector on Voyager 1 malfunctioned in 1980, just a few years after launch. Instead, scientists measured the magnetic field of the Sun and of the interstellar wind. The change did not manifest as expected, so scientists could not draw a definite conclusion. Another set of instruments on board, two antennae, are able to measure plasma—but only if it is moving in waves. A solar eruption in March 2012 sent a shock wave that took 400 days to reach Voyager, but caused the plasma to react in a way that Voyager could detect. This signal finally enabled the confirmation of the craft’s passage into interstellar space.

Sadly, our connection with Voyager will eventually end as its power runs out (its current power output is about that of a refrigerator lightbulb—try detecting that from 11 billion miles away!) The craft is expected to lose all power and cease its communications with Earth by 2025. With no friction to slow it down, however, Voyager will continue to drift on, indefinitely. It remains well within the sphere of the Sun’s gravitational dominion, but will take about 30,000 years to pass through the Oort cloud, the cometary halo extending about a light year or so from the Sun and the farthest-known objects orbiting the Sun. So although the plucky spacecraft has entered interstellar space and left the Sun’s magnetic influence, the Voyager team says it will not yet leave the Solar System until it passes through the Oort Cloud. Beyond that, it will take another 70,000 years to travel the 4.3 light year distance between us and the next closest star, Alpha Centari.

But let’s not underestimate the significance of this event. A man-made object has left the confines of the tiny speck of our galactic home for the very first time and entered the space between stars. We have physically entered a space greater than any explored before and taken the first step in ever visiting other star systems. True, it is a mere 16 light hours, but substantially farther than the 1.3 light seconds to the Moon, which is the farthest that humans have gone.

Voyager leads the way in a whole new frontier of exploration.

Elise Ricard is the Senior Presenter at the Morrison Planetarium and holds a master’s degree in museum education.

Recently, the search for extrasolar planets (a.k.a. exoplanets) has centered around finding an Earth-like world, a place where life as we know it could exist. After all, wouldn’t it be exciting to discover extraterrestrials—or at least a new place humans could inhabit? Problematically, these small, potentially inhabitable planets are terribly challenging to detect. Twenty years of searching has yielded 941 (and counting) confirmed planets, but none very much like Earth… Although we are well on our way to finding such a “Goldilocks” world (not too hot, not too cold, but juuuust right), other, often larger exoplanets are proving easier to find and uniquely interesting.

A significant percentage of the exoplanets uncovered so far are “hot Jupiters”—colossal gas giant worlds that equal or surpass the mass of Jupiter and orbit very close to their parent stars, creating high surface temperatures as a result. One particularly interesting giant is HD 189733b, a massive world a mere 63 light years away. Though discovered in 2005, its proximity to our solar system makes it a good exoplanet to examine.

Some of the more interesting recent studies of this exoplanet leave behind the question of habitability to examine different planetary characteristics. In 2008, astrophysicists used polarimetry to detect and monitor the planet in visible light and determined an overall color of the world as it would appear to us. A second set of independent tests came back just this last month with the same result. The planet, as we would perceive it, is cobalt blue!

The discovery of another blue marble in the Milky Way is enticing. But this blue color is obviously not due to liquid oceans covering its surface. So where is the color coming from? It could be caused by a slow shower of molten glass. Observations have shown the likely presence of silicate particles in the lower atmosphere. This would scatter light in such a ways as to appear blue in the visible spectrum. Silicate is a component of glass which has lead some researchers to suspect the atmosphere might rain intensely heated bits of molten glass. Certainly not a storm you would want to be caught in!

Looking closer at the planet, all similarities to Earth continue to sizzle away. Orbiting 30 times closer to its star than Earth is to the Sun (which works out to about 13 times closer to its star than Mercury is from the Sun), this planet definitely qualifies as a HOT Jupiter: 1,200°F (650°C) on the night side to 1,700°F (930°C) on the day side with winds as fast as 6,000 miles per hour (nearly a thousand kilometers per hour). This is not a life-friendly place. In fact, Scott Wolk of the Center for Astrophysics estimates the atmosphere of the planet is boiling away at about 660,000 to 100 million tons of mass per second.

HD 189733b is a fantastic example of the surprises that continue to amaze us as we learn more about our universe. Hot Jupiters are not places we study in the hopes of finding life. Rather, we explore these fascinating places so different from our own world to learn about the diversity of planetary systems in our galaxy. They help us uncover more about the evolution of planets and allow us to probe the conditions that came together to form the immense diversity of worlds that we see. They provide clues and contrasts to our own planet, where the processes of life were able to take hold and evolve.

Could Earth have once been a hot Jupiter instead? Quite unlikely. Can HD 189733b ever be the next Earth? Not likely. But these bizarre and far-off worlds are certainly engaging in their own right.

Elise Ricard holds a master’s degree in museum education and is a presenter at Morrison Planetarium.

Images: X-ray: NASA/CXC/SAO/K. Poppenhaeger et al; Illustration: NASA/CXC/M. Weiss

Mark Showalter and his research team at the SETI Institute in Mountain View, California, are on a roll. They’ve shown us yet again how much we have to learn about our closest planetary neighbors.

In 2011 and 2012, Showalter’s team discovered two additional moons orbiting Pluto. (The International Astronomical Union recently decided on the names Kerberos and Styx for these moons, despite an overwhelming public vote to name one of them Vulcan.) Using the Hubble Space Telescope, the same researchers recently discovered a new moon orbiting Neptune.

“I got nice pictures of the arcs [segments of the planet’s rings], which was my main purpose, but I also got this little extra dot that I was not expecting to see,” says Showalter.

At 65,400 miles from Neptune, the speedy, newly-discovered moon completes an orbit every 23 hours. This moon is hard to track, but more than 150 archived images from Hubble between 2004 and 2009 enabled Showalter to track down the orbit of the new moon.

“The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system,” he says. “It’s the same reason a sports photographer tracks a running athlete—the athlete stays in focus, but the background blurs.” (Showalter compares capturing the new moon to Eadweard James Muybridge’s famous racehorse photographs in a blog post earlier this week.)

This 12-mile wide moon is the smallest of the Neptunian system (which currently includes 14 moons), and revolves around Neptune between the orbits of Larissa and Proteus. For now the tiny dot is called S/2004 N 1. The official name may not be put to vote this time (but Star Trek fans can get cracking on ideas).

S/2004 N 1’s discovery brings up additional questions besides its new name. A mini moon like this should have had trouble forming in the neighborhood of much larger moons.

“How you can have a 20-kilometre object around Neptune is a little bit of a puzzle,” says Showalter. “It’s far enough away that its orbit is stable. Once you put it there it will stay there. The question is, how did it get there?”

Triton is Neptune’s biggest moon, orbiting in the direction opposite Neptune’s spin. Astronomers originally thought that a moon of this type would have to be captured by Neptune’s gravity, destroying all smaller moons in the process.

Stay tuned to learn S/2004 N 1’s new name, and perhaps new theories about how it originated in the first place!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA, ESA, M. Showalter

Recent research makes it seem like astronomers can’t look up without finding exoplanets. Data illustrate scores of super earths, planets in their habitable zones, and multiple-planet systems… But a specific type of planet has proven elusive: a planet orbiting at a considerable distance from its parent star.

Gemini Observatory’s Planet-Finding Campaign recently completed the most extensive direct imaging survey to date, but the results were mostly devoid of large planets—especially gas giants—at significant distances from their parent stars. This may seem counter-intuitive… After all, we think of our own solar system as ordinary or average, and it includes giant planets such as Uranus and Neptune, which orbit quite far away from our sun.

Michael Liu, leader of the Gemini Planet-Finding Campaign, sums up the situation this way: “We’ve known for nearly 20 years that gas-giant planets exist around other stars, at least orbiting close-in. Thanks to leaps in direct imaging methods, we can now learn how far away planets can typically reside. The answer is that they usually avoid significant areas of real estate around their host stars. The early findings, like HR 8799, probably skewed our perceptions.”

Exoplanet discoveries are usually based on data taken from the parent star, but HR 8799 was one of the first star systems observed directly from Earth. Using the Gemini telescope, researchers could see gas-giants at large orbital distances from their sun. At the time of discovery in 2008, they did not have enough background knowledge to realize that HR 8799 was very, very unusual.

But gas giants aren’t missing; they just tend to cling to their parent stars in a close orbit. And this lack of distant gas giant planets is apparent across all sizes and types of stars.

Difficulty finding planets at distant orbits has a silver lining, because absent planets can actually tell us more about planet formation. Astronomers are developing an explanation for the strange holes in dust disks surrounding young stars. “It makes sense that where you see debris cleared away that a planet would be responsible, but we did not know what types of planets might be causing this. It appears that instead of massive planets, smaller planets that we can’t detect directly could be responsible,” said Zahed Wahhaj of the European Southern Observatory.

Even though the missing planets have taught us something, the search for planets with orbits similar to that of Uranus and Neptune continues. And we thought we lived in an average solar system…

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image credit: NASA/ESA/C.Carreau

Early last week I wrote an article about how new data from Voyager 1 shed light on the structure of the Sun’s heliosphere and solar wind. Just a few days after that, researchers announced evidence of Earth’s own space wind!

Scientists proposed the existence of a space wind surrounding Earth about 20 years ago, but direct detection has eluded scientists until now.

Earth is surrounded by a magnetic field that encloses our magnetosphere. The plasmasphere is the inner part of that magnetosphere, and it looks a giant donut made of electrically-charged particles called (as its name suggests) plasma.

The Sun’s magnetic activity can accelerate plasma toward Earth, which impacts our magnetosphere. During such solar storms, we have observed plumes of material transfer between the plasmasphere and the outer magnetosphere, but researchers also proposed the existence of a steady flow of plasma that occurs around the clock. After years of theoretical work, Iannis Dandouras of the Research Institute in Astrophysics and Planetology in Toulouse, France, has directly detected this wind in data from the European Space Agency’s Cluster spacecraft.

Dandouras measured the properties of charged particles in the plasmasphere to find that the forces governing plasma motion exist slightly out of balance, forming a steady wind.

“After long scrutiny of the data, there it was, a slow but steady wind, releasing about one kilogram of plasma every second into the outer magnetosphere. This corresponds to almost 90 tons every day. It was definitely one of the nicest surprises I’ve ever had!” said Dandouras.

Don’t worry, the plasmasphere won’t evaporate away: it also refills. Dandouras reassured everyone that “due to the plasmaspheric wind, supplying plasma—from the upper atmosphere below it—to refill the plasmasphere is like pouring matter into a leaky container.”

Michael Pinnock, Editor-in-Chief of Annales Geophysicae, recognizes the importance of the new result. “It is a very nice proof of the existence of the plasmaspheric wind. It’s a significant step forward in validating the theory. Models of the plasmasphere, whether for research purposes or space weather applications (e.g. GPS signal propagation) should now take this phenomenon into account.”

We can even apply our understanding of Earth’s plasmaspheric wind to other places. Why wouldn’t another planet such as Jupiter or Saturn experience the exact same phenomenon? The Solar System could be a very windy place!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA

Cause for celebration! The 10,000th near-Earth object (NEO) has been discovered.

Asteroid 2013 MZ5 joined the ranks of asteroids and comets whose orbits pass near Earth. On an astronomical scale, “near” means within 28 million miles…

The Near-Earth Object Program looks for all NEOs, especially large ones with the potential to harm Earth (called a Potentially Hazardous Asteroid). This type of candidate would need to be at least about 100 feet (about 30 meters) across to do significant damage a populated area—and about 3,200 feet (nearly a kilometer) in diameter to cause global devastation.

As you might expect, large asteroids are easier to find than small ones. NASA estimates that we have discovered all but a few dozen of the largest asteroids, those 460 feet (140 meters) in diameter or larger. (Whew!) Therefore, NASA is shifting its attention to medium-sized threats. If 90% of these were found, the threat of an unexpected impact would be greatly reduced, perhaps even to one percent!

“Finding 10,000 near-Earth objects is a significant milestone,” said Lindley Johnson, program executive for NASA’s Near-Earth Object Observations Program. “But there are at least 10 times that many more to be found before we can be assured we will have found any and all that could impact and do significant harm to the citizens of Earth.”

Discovered by the Pan-STARRS-1 telescope in Hawaii, this new asteroid is about 1,000 feet in diameter. That would put it in a pretty dangerous category if it were headed toward Earth, but its orbit does not pass close enough to us to be a significant threat.

“The first near-Earth object was discovered in 1898,” said Don Yeomans, manager of the Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory. “Over the next hundred years, only about 500 had been found. But then, with the advent of NASA’s NEO Observations program in 1998, we’ve been racking them up ever since. And with new, more capable systems coming on line, we are learning even more about where the NEOs are currently in our solar system, and where they will be in the future.”

A privately-funded mission called Sentinel might extend the search with a space-based telescope that will likely identify hundreds of thousands of NEOs. You can watch Science Today story on Sentinel or watch an animation narrated by former astronaut Ed Lu describing the mission.

10,000 down, how many to go…?

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: PS-1/UH

Earth’s neighborhood just got a little larger.

Astronomers thought that Earth was located on a spur of an arm of the Milky Way… until data from the Very Long Baseline Array telescopes suggested that we could be located closer to the center.

While it’s simple to observe a bird’s-eye view of other galaxies, models of the Milky Way are inaccurate due to Earth’s limited vantage point. We are attempting to measure an entire galaxy using only Earth’s narrow perspective, and at the center of our galaxy is a large bulge, blocking about half of the Milky Way from view.

To make the best model possible, astronomers use a technique called parallax. Measurements are taken from locations on either side of the sun to give multiple perspectives of our location in the sky. Then, astronomers use trigonometry to calculate where we might reside in comparison to distant objects.

At the center of the Milky Way is a supermassive black hole, whose gravitational pull is capable of keeping 200–400 billion stars in orbit around the galaxy. Measurements from NASA’s Spitzer Space Telescope revealed that these stars are oriented in two arms that spiral around the black hole.

“Based on both the distances and the space motions we measured, our Local Arm is not a spur,” said Alberto Sanna, a postdoctoral fellow with the Max-Planck Institute for Radio Astronomy (MPIFR). “It is a major structure, maybe a branch of the Perseus Arm, or possibly an independent arm segment.”

Sanna and his colleagues presented their research this week at the American Astronomical Society meeting, held in Indiana.

Astronomers are creating increasingly accurate models of the Milky Way and every new finding tells us more about the entire universe.

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA

Launched in 1977, Voyager 1 is the most distant human-made object in our galaxy, and is close to passing beyond the limits of our solar system.  This week, the team announced that Voyager 1 has entered the “magnetic highway,” a region between the heliosphere and interstellar space. Scientists coined the new term “magnetic highway” to describe the place where the Sun’s magnetic field lines connect with interstellar magnetic field lines. As Stone said at yesterday’s meeting, “The new region isn’t what we expected, but we’ve come to expect the unexpected from Voyager.”

Voyager has three instruments on board to measure changes in the magnetic environment—one that detects the low-energy particles that come from the solar wind within the heliosphere; one that detects the high-energy particles from interstellar space (remnants from supernovae explosions millions of years ago); and a magnetometer, which measures the strength and direction of magnetic fields.

How do the scientists know the magnetic highway isn’t just interstellar space? First, both low- and high-energy particles are detected.  Also, the magnetic field from the Sun runs east to west, and that should change dramatically once the spacecraft enters interstellar space.

Voyager 1 first merged onto this highway in late July, but then quickly exited. The same thing happened in early August, and finally Voyager entered for good in late August. Stone predicts that interstellar space can’t be too far for Voyager 1. “We believe this is the last leg of our journey to interstellar space,” Stone said. “Our best guess is it’s likely just a few months to a couple years away.” (Hopefully well before the spacecraft’s power is due to shut off in 2025.)

Because Voyager 1 is now located about 11 billion miles away from the Sun, the signal from the spacecraft takes approximately 17 hours to travel to Earth. Voyager 2, the longest continuously operated spacecraft, is about 9 billion miles away from our sun, headed in a completely different direction. While Voyager 2 has seen changes similar to those seen by Voyager 1, the changes are much more gradual. Scientists do not think Voyager 2 has yet reached the magnetic highway.

The latest Mars rover, Curiosity, will soon begin its adventure on the Red Planet! Curiosity will land in Gale Crater this August 5th.

With less than a month before Curiosity’s landing, Dr. David Blake gave a Benjamin Dean Lecture at the California Academy of Sciences on July 9th, 2012. A senior staff scientist in the Exobiology Branch at NASA Ames Research Center, Dr. Blake designed one of Curiosity’s science instruments, CheMin (Chemistry and Mineralogy).

CheMin will use X-ray diffraction to measure the mineral structure in samples of Mars dust: an X-ray beam shot through a dust sample will scatter in a distinctive pattern that depends on the arrangement of atoms and molecules present in the sample. CheMin also measures the energy of individual X-ray photons to determine what elements make up the sample.

Other important instruments onboard Curiosity will photograph the rover’s surroundings, drill into rock samples, look for traces of organic compounds, and conduct a variety of experiments that earned Curiosity its original name, “Mars Science Laboratory.”

The 900-kilogram roving laboratory requires a landing sequence different from previous, smaller rovers’ landings. Smaller rovers descended to the Martian surface protected by giant airbags, bouncing to a stop before deflating the airbags and beginning operations. Curiosity needs to complete an elaborate series of steps nicknamed the “Seven Minutes of Terror,” so called because NASA engineers have no way to control what happens during the seven minutes it takes the spacecraft to traverse the thickness of the Martian atmosphere. Dr. Blake showed the audience an interesting clip of the simulated landing process…

After its eight-month journey from Earth, the capsule is racing toward Mars. The Aeroshell, on the outside, includes a heat shield that protects the craft during its initial entry into the Martian atmosphere. At a designated point in its descent, the Aeroshell deploys a parachute. The heat shield drops away, and the Sky Crane carrying the rover then separates and executes a controlled descent under its own power before deploying a cable to lower the rover down to a carefully selected landing site. Flight engineers have refined Curiosity’s landing site during the eight-month voyage, pinpointing a relatively small area inside Gale Crater.

For the first few months that Curiosity is surveying Mars, Dr. Blake will live on “Mars time.” The days on Mars are about 40 minutes longer than our 24-hour Earth day, and scientists and engineers will adjust to the longer day, working on the same schedule as the rover. But all this extra time definitely adds up: Dr. Blake compares it to shifting a time zone a day for the duration of the switch, and when he practiced living on Mars time for a week, he didn’t relish the experience.

Keep up to date with Curiosity’s progress here!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and volunteers for the Morrison Planetarium.

Image credit: NASA/JPL-Caltech

It was a weekend full of aliens and black hole theories at the Hyatt Regency in Santa Clara, California. Scientists, professors, artists, authors, and science enthusiasts gathered for SETIcon II, a conference organized by the SETI Institute to learn about and celebrate recent developments in the search for extraterrestrial intelligence.

The conference consisted of a series of panels discussing everything from potential asteroid resources to Hollywood Sci-Fi movies.

Each discussion had a diverse set of panelists that complimented each other—each speaker with a different background, adding different perspectives to each panel. For example, in a panel titled “Black Holes in Space—Hearts of Darkness”, Robert J. Sawyer, Andre Bormanis, Alex Filippenko, and Leonard Mlodinow discussed theories about black holes while also calling upon movies and books to identify and clarify any misconceptions.

Alex Filippenko, Seth Shostak, Richard Rhodes, and Marc Okrand even discussed religion (with much sensitivity… especially because SETI has been accused of being a religion) during the “Did the Big Bang Require a Divine Spark?” panel.

The panelists Cynthia B. Phillips, Mark R. Showalter, and Charles Lindsay informed the audience about planetary art in “The Magnificence and Majesty of the Outer Solar System” while a slideshow of the artfully embellished planets played in the background.

In addition to the regular excitement about science, the conference was heavily fueled by Kepler’s recent success. The Kepler telescope is currently looking for planets in the habitable zone, because these planets are likely to be more earth-like and therefore more likely to be suitable for life.

The telescope has already found over 2,000 transiting planets, an abundance that led NASA to approve the extension of the Kepler mission until 2016. The panelists could not hide their enthusiasm: such success in the search for extraterrestrial intelligence is worthy of celebration.

The conference also included an evening honoring Jill Tarter, director of the search for intelligent life and inspiration for Jodie Foster’s role in the movie, “Contact”.

Whether a Battlestar Galactica enthusiast or a NASA researcher, it was truly a conference for everyone.

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and volunteers for the Morrison Planetarium.