Science

Patrick Rowan's Skywatch: Voyager's 40th anniversary, first interstellar asteroid


My commitment in these pages to this past summer’s total solar eclipse and other topics, led me to brush aside a very important space anniversary: The launch 40 years ago in September of the twin Voyager spacecraft on their historic journey through the outer solar system.

The epic journeys of Voyagers 1 and 2 gave us the solar system we know today, along with a few extra surprises. Voyager 1, the farthest human-made object from Earth, has now actually exited the solar system into interstellar space.

My plans for this column about the Voyagers were disrupted by news of the discovery of the first object known to come from outside our solar system. Although it’s probably not aliens, some aspects of the object and its discovery are eerily similar to those described in Arthur C. Clarke’s Rendezvous with Rama, one of the first science fiction stories I ever read.

This and the Voyager story, however unrelated, do remind me of how perceptions of “our world” have expanded. We’ve begun sending things out of our solar system, and noticing things coming in. This is human awareness on a whole new scale.

When Voyager 1 sailed out of the heliosphere — the bubble around the sun formed by the solar wind — on August 25, 2012, it became the first craft from Earth to reach interstellar space, making the Voyager missions as significant in the history of Earth as when American engineers first punched through Earth’s atmosphere into space with a German V2 rocket in 1944, or the Russians successfully boosted Sputnik into orbit in 1957.

We remain in touch with Voyager 1, and two of the four other spacecraft also headed out of the solar system: Voyager 2, and New Horizons (which gave us our first close look at Pluto just two years ago.) Pioneers 10 and 11, launched in 1972 and 1973, fell silent in 2003, and 1995. All of these will make it to interstellar space, we just don’t know exactly when.

The Voyagers’ primary missions were to explore the outer planets, the gas giants. In 1979, Voyager 1 zipped past Jupiter, and Saturn in 1980. Voyager 2 did the same in 1979 and 1981, then continued on its “Grand Tour” of the solar system’s planets to Uranus in 1986, and Neptune in 1989. It is still the only craft ever to visit those two.

Before then, Uranus and Neptune had been seen only as small discs through the best telescopes on Earth’s surface. It would be another couple of years before the Hubble Space Telescope began spoiling us with it crisp celestial views from above the interference of the atmosphere which gives us pretty twinkling stars, but makes telescopic views look watery and blurred.

A year after the Voyager 2’s Neptune encounter, Voyager 1 gave us its most enduring legacy. At the urging of the late visionary Carl Sagan, NASA agreed to point that craft’s cameras back for some parting shots of the planets before turning them off for good.

Little could be seen from 3.7 billion miles away, more than 40 times Earth’s distance from the sun, and some scientists saw little or no value in the exercise. Fortunately, the few who saw the absurdity in not taking pictures, given how long it might be before we got a camera out that far again — if ever — won the day, and in 1990, the iconic “Pale Blue Dot” image of Earth was created.

The image data, transmitted via radio signal, travelling at the speed of light, took nearly five and a half hours to cover the distance from Voyager to Earth.

The Voyagers represent our single grandest triumph in exploration of the gas giants and their moons. The fact that we’re still sending commands to, and receiving useful data from these machines after all these years is a stunning achievement for the robust 1970’s technology, and a testament to the scientists and engineers who were so committed to this endeavor’s success.

Now, Voyager 1 is more than 140 times farther away from the sun than we are on Earth, and Voyager 2 is 116 times farther. Check their real-time status updates at:
https://voyager.jpl.nasa.gov/mission/status/

Even after the radioisotope thermoelectric generators (RTGs) powered by plutonium-238  fall below useful levels, and we finally lose touch with our emissaries, which will probably happen sometime in the next 10 years, the Voyagers will still serve a purpose.

Not only do they carry gold records with images, music, and greetings from Earth, each also serves as a vessel for the human spirit, and a physical manifestation of our dreams of  exploration, and a reminder of humanity’s need for humility.

Given the vastness of the Milky Way, it seems unlikely either craft will be discovered by some alien race, but they have a lot more time than our world does, which increases the chances. In a billion years — after the sun has toasted the Earth and itself flamed out — the Voyagers will still be on their journey into the great unknown.

Will we be setting anything else adrift in the cosmic sea, and when? Have other civilizations done anything similar?

In October, astronomers discovered an object unlike anything seen before. It was first thought to be a comet, but the lack of any coma or tail swept behind it by the solar wind forced a reclassification. Further measurements revealed that — to paraphrase the title of the classic 1953 science fiction film — “It came from interstellar space!”

Regardless of whether or not it’s an alien artifact, the discovery of ‘Oumuamua (officially 1I/2017 U1) — the first interstellar object ever observed passing through our solar system — sent astronomers into high gear seeking better data.

Although it came from the direction of the star Vega, which is visible in the west early these evenings, at about 57,000 mph, it would be difficult to determine its origin. If it had come from the fringes of our solar system, it should have out-gassed like a comet when close to the sun.  

Perhaps the next most striking aspect of the object is its shape, maybe ten times as long as it is wide, something never before seen in our solar system. Estimates vary, but a good guess puts it at about half a mile long, and a tenth as wide… much smaller than the Rama’s 30 mile-long cylinder.

Unlike the alien ship in Clarke’s Rendezvous with Rama, which rotates along its axis to create artificial gravity on the interior, ‘Oumuamua tumbles end-over-end.

It would be easy to calculate the g’s generated by the objects tumble, but its cigar-shape would require high tensile strength to keep from flying apart, and that means it could be made of solid rock or metal. The fairly uniform reddish color is less curious, being common among long-duration asteroids.

The object was already on its way out when discovered, so there’s little chance of sending a probe to catch up with it.

Find rise and set times for the sun and moon, and follow ever-changing celestial highlights in the Skywatch section of the Weather Almanac in The  Republican and Sunday Republican.

Patrick Rowan has written Skywatch for The Republican since 1987 and has been a Weather Almanac contributor since the mid 1990s. A native of Long Island, Rowan graduated from Northampton High School, studied astronomy at the University of Massachusetts-Amherst in the ’70s and was a research assistant for the Five College Radio Astronomy Observatory. From 1981 to 1994, Rowan worked at the Springfield Science Museum’s Seymour Planetarium, most of that time as planetarium manager. Rowan lives in the Florence section of Northampton with his wife, Clara.

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