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.

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

The third Thursday of every month, the Morrison Planetarium hosts “Universe Update” at the 7:30 and 8:30 planetarium shows during NightLife. I select my favorite astronomy stories from the past month, and I give a brief run-down of current discoveries while taking audiences on a guided tour of the Universe. Y’see, the planetarium sports a tricked-out three-dimensional atlas of the Universe, so I can take you places virtually while talking about the latest astronomy news.

I always start at Earth and work my way out to cosmological distances, so I’ll list the news stories in the same order—from closest to farthest from home.

A mere 400,000 kilometers (give or take) from Earth, NASA’s Lunar Reconnaissance Orbiter (LRO) just completed the exploration phase of its mission and will now begin its science mission: take a look at the official release for more details. But basically, this means that they’re going from a mission dedicated to find places to visit (the so-called exploration phase) to a mission dedicated to producing results of scientific interest. As part of the hand-off, a press conference highlighted some of the most exciting results from the mission’s first year.  Check out Thursday’s Science Today blog for more details.

Also in honor of Earth’s nearest celestial neighbor, you can celebrate International Observe the Moon Night this Saturday. NASA got so excited about it they actually had a press release describing the international character of the event. For those in San Francisco, you can check out the event at Land’s End hosted by the San Francisco Amateur Astronomers (a.k.a. the SFAA).

Moving on to Mars… The Phoenix lander may have ended its mission a while ago, but sifting through data sent back by the lander has revealed fascinating details about Mars’s watery past. Liquid water, it seems, remained fairly close to freezing during most martian history—no Yellowstone on the Red Planet! This could have interesting implications for the likelihood of life on Mars.

As you may recall from fifth grade, asteroids fill orbits between Mars and Jupiter. What you may not have learned is that some asteroids travel in pairs, orbiting one another like Ida and Dactyl. Astronomers have now matched theory to observation, suggesting that bigger asteroids can give birth to smaller satellites, but the smaller ones are never more than 40% the size of their parent asteroid.  Details here.

During last night’s program, I completely forgot to describe a terribly exciting result announced earlier in the month: a new way to weigh planets! Typically we determine the masses of planets by studying orbital dynamics: the motion of moons in a planetary system or the trajectories of spacecraft interacting with a planet. Turns out that works pretty well, but the new technique could provide more accurate results for some planets. Radio astronomers used variations in the observed timing of pulsars to refine estimates of the mass of planetary objects in the Solar System. If you really want to geek out, take a look at the original paper describing the results!

Mentioning Pluto in any planetarium show always elicits a reaction, so I try to bring it up whenever I can. People should really just learn to let go, ’cuz hey, Pluto’s in good company: Kuiper Belt Objects (KBOs), Trans-Neptunian Objects (TNOs), and other acronyms share its orbital space, so we don’t need to feel too sorry for the supposedly demoted planet. Not like it’s lonely out there. Germane to that point, the Hubble Space Telescope just reported the discovery of more playmates for Pluto in the form of fourteen elusive TNOs.

And just for kicks, before we head any farther from home, you might want to check out a tour of recent images from around our Solar System.

In news about stars, the CoRoT spacecraft used “stellar seismology” to detect regions of magnetic activity on a star almost 100 light years away.  According to the press release, observations suggest that the star goes through cycles much like the Sun, but much more quickly… The Sun takes eleven years to go from solar maximum to solar minimum, but the attractively-named HD49933 does the same thing in less than a year! Et si vous parlez français, vous pouvez lire le communiqué de presse.

Another orbiting observatory, the Spitzer Space Telescope, provided observations of a star with a disk of material surrounding it—a disk that could eventually form planets. And we all love planets! (At least those of us who live on them.) What astronomers found interesting was that the disk seems to contain phyllosilicates, which could provide a carrier for water that could form oceans on the surfaces of distant worlds. A long chain of reasoning (phyllosilicates in disk that could form planets that could end up with oceans filled with water packed into phyllosilicates), but tantalizing nonetheless. (Believe it or not, by the way, astronomers actually have entire conferences devoted to topics such as “The Delivery of Volatiles and Organics.” How cool is that?)

From the ground-based Keck Observatory comes a remarkable surprise: astronomers managed to take the spectrum of an extrasolar planet! Of the 490-some-odd known planets, only six have been imaged, so this is quite an achievement. Not surprisingly, the spectrum threw astronomers for a loop, revealing a planet much hotter than they expected.

A case of stellar cannibalism made the headlines like any good violent crime: you can read about the shocking events direct from the source, from the BBC, or from Wired Magazine.

I didn’t mention them during last night’s show, but Princeton released some spiffy new supernova simulations. Oooh, pretty!

Also pretty, this image of NGC 300 from the European Southern Observatory. Galaxies such as NGC 300 have “low surface brightness,” which means they look rather diffuse and faint. Astronomers exploring the faintest of the faint managed to reveal relationships between galaxies—tendrils of gas that link tiny dwarf galaxies with more massive spiral galaxies in close proximity. The conclusion? Something that astronomers have suspected for quite some time: spirals eat dwarfs. Stellar cannibals and voracious galaxies? Who knew that celestial objects exhibited such ravenous behavior?

Hungry spirals might also consider consuming these particularly appetizing-sounding neighbors: Green Pea Galaxies! Amateur scientists working with GalaxyZoo identified these oddball galaxies in 2007, and astronomers have recently announced some ideas as to the nature of these phenomena. Quite a victory for citizen scientists!

Finally, I’ll wrap up with the wildest announcement of the month, the suggestion that at least one fundamental constant might be changing over regions of space. Fundamental constants, as you might guess from the name, tend to remain pretty reliable players in equations that describe the behavior of objects in the Universe.  The particular “constant” in question, the fine-structure constant, has inspired suspicions about its constancy for a while, and astronomers are suggesting that its value billions of light years away (around the energetic cores of young galaxies known as quasars) might differ from what we measure here on Earth.

Those rate as my favorite stories for the last month.  Stay tuned for next month’s “Universe Update.”

Ryan Wyatt, Director
Morrison Planetarium and Science Visualization