A Pale Blue Glow

by Shane L. Larson

One of the great things about being a scientist is I’m exposed to amazing and awesome things. Every. Single. Day. Sometimes I am astonished by Nature itself, and other days I am amazed by our ingenuity and abilities as we come of age in the Cosmos. Today was one of those days.

The first picture of the Moon and Earth together in space, taken by Voyager 1.

This story has its origins long ago. On 5 September 1977 we hucked a 722 kg spacecraft into the sky, named Voyager 1. That was the last time any of us ever saw Voyager 1 with our own eyes. But Voyager has been on a 37-year journey to act as our eyes in the Solar System. On 18 September 1977, barely 13 days after launch, when it was 7.25 million miles from Earth, Voyager sent home the first picture ever of the Earth and Moon together in space. It went on to Jupiter, where it took pictures of clouds and storms that look for all the world like the finest paintings on Earth, and discovered the first active volcanoes beyond the Earth on the enigmatic moon Io. At Saturn, it returned the first high-resolution images of an exquisite ring system, and showed us a shattered Death Star like Moon known as Mimas, dominated by an enormous crater named Herschel. But for all the wondrous pictures, we never saw Voyager. Like your Mom taking pictures of your childhood, we have never once seen the photographer chronicling our growth.

Just a sample of the kinds of discoveries made by Voyager 1. (TopL) Exquisite cloud structure on Jupiter. (TopR) Active volcanism on Jupiter’s moon, Io. (BottomL) Tremendous structure in Saturn’s rings. (BottomR) Saturn’s moon, Mimas.

But today, I saw something that made me smile. Since it began its long outbound journey, we’ve been talking with Voyager 1 on a radio. In all, it only transmits about 20 watts of power, something typical of a larger compact-fluorescent-lightbulb. The total power received on Earth from Voyager is about a ten-billionth of a millionth of a watt. In one second, we receive less than a trillionth the energy a single snowflake delivers to your shoulder as you’re walking to work.

VLBI image of Voyager 1, diligently beaming its signal back to Earth.

But take a look at the picture above, released by NASA last fall. See that pale blue dot right there? That is Voyager 1, seen through the eyes of the Very Long Baseline Interferometer, an array of linked radio telescopes that stretches from one side of the Earth to the other. It sees the sky in radio light. Normally it looks at quasars and distant nebulae, but this image is of Voyager 1, shining its radio back at Earth. This is the first radio signal of human origin ever to be received from outside the solar system. It is also the first picture of Voyager 1 taken since its launch. It’s a bit like seeing your friend in the dark, waving their cellphone at you from a distant mountaintop.  But it’s there, and we can see it — the pale radio beacon of Voyager 1, drifting alone in the immense dark between the stars.

Long after it runs out of power, Voyager 1 will continue to drift alone through the galaxy.

What will happen to Voyager 1? It will continue to talk to us for a little while longer. It is powered by a small nuclear power plant, gleaning energy from the decay of plutonium. But that energy supply is dwindling, and sometime around the mid 2020’s, just more than a decade from now, Voyager 1 will fall silent. The pale blue glow will disappear forever; there will be no more pictures of our loyal emissary. Voyager 1 will continue onward however, bound for the depths of the galaxy, a dead hulk built by a race of curious lifeforms that call themselves “humans.”

But now this has me thinking. All of our knowledge of the outer solar system has been gleaned with telescopes, and with robotic emissaries.  None of the sights you have seen in pictures has ever been witnessed directly by human eyes. Not the dual-tone colors of Saturn’s enigmatic moon Iapetus; not the spider-web of canyons in Mercury’s Caloris Basin; not the misty depths of the Valles Marineris on Mars. Instead, Casinni has been twirling through the Saturn system for almost a decade, and has returned the highest resolution images of Iapetus we’ve ever seen.  Mercury MESSENGER, only the second spacecraft ever to visit Mercury, finally arrived in 2011 and sent high resolution images of the Spider Crater back to Earth. And Mars? Well, Mars has its own fleet of orbiting satellites and ranging rovers to investigate its mysteries.

(L) Saturn’s moon Iapetus has a light and a dark side. (C) The Spider Crater on the floor of Mercury’s Caloris Basin. (R) Fog in the Valles Marineris on Mars.

What happens to all our tiny robots, sent out into the Cosmos all on their own? We’ve been tossing them into space almost non-stop since the start of the Space Age — what happens to all of them?

Only 5 will ever travel beyond the solar system. Pioneers 10 and 11 are both bound for interstellar space, now quiet and dead after their power supplies failed in 2003 and 1995. Voyager 1 and 2, having completed their Grand Tour of the outer solar system, are also outbound; we expect to lose contact with them within the next 10 to 20 years. And lastly, there is New Horizons, bound for Pluto and the Kuiper Belt beyond. It is by far the youngest of this august group of explorers. It was designed to have power for 20-25 years, but it has already spent the last eight-and-a-half years just getting to Pluto — it should last another 15 years or so.

Spacecraft that are going to escape from the solar system. (L) Pioneer (C) Voyager (R) New Horizons

(T) When Spirit got stuck on Mars, NASA engineers recreated the situation on Earth, trying to figure out how to free the rover. (C) Artist’s imaging of what Galileo looked like as it burned up in the Jovian atmosphere. (B) The LCROSS mission before impact.

Many of our robots, like the Voyagers and Pioneers, will just die. This famously happened to the Spirit rover on Mars. It trundled around the Martian surface for 2269 days (perhaps, some say, trying to earn a trip back home) before we lost contact with it. Spirit had become stuck in a Martian sand dune and was unable to free itself. Stuck on flat ground, unable to tilt itself toward the Sun to keep warm in the cold Martian winter, we last spoke with Spirit on 22 March 2010.

The Galileo mission, which spent more than seven-and-a-half years exploring the Jovian system, was crashed into Jupiter, to prevent it from tumbling out of control when its power failed, possibly contaminating a moon like Europa, where we can imagine extraterrestrial life may exist. On 21 September 2003, it was plowed into Jupiter. We couldn’t see it take the final plunge, but we listened to it faithfully radioing us everything it could for the last few hours before its end.

Sometimes, we crash our spacecraft on purpose, for science! One of the most spectacular examples of the was LCROSS, the Lunar Crater Observation and Sensing Satellite. The goal of this mission was to look for water ice in the perpetually shadowed craters on the surface of the Moon; water on the Moon would have important implications for the sustainability of lunar colonies. LCROSS had two pieces — it’s Centaur rocket stage, and the Shepherding Spacecraft that carried the science instruments. On 9 Oct 2009, the Centaur rocket impacted the Moon at a speed of about 9000 kilometers per hour; the Shepherding Spacecraft flew through the cloud of debris and radioed the composition back to Earth. This exquisitely timed dance was a planned suicidal flight for the Shepherding Spacecraft; its unavoidable fate was to impact on the Moon about 6 minutes after the Centaur stage. The result? There is water, frozen in the lunar soil.

But the saddest fate to me, is that of Mercury MESSENGER. MESSENGER was the first spacecraft to visit Mercury since Mariner 10 flew by three times in 1974. Despite three passes, Mariner 10 only mapped out about 45% of the surface; until MESSENGER’s arrival in 2011, we had no idea what more than half of Mercury looked like.  It took MESSENGER 7 years to get to Mercury. It has been there for about three-and-a-half years at this point, and we are looking ahead to the end. Over time, the closest point of MESSENGER’s orbit has been getting lower and lower, affording us the opportunity to understand Mercury’s gravitational field and to map and  probe the surface of Mercury with exquisite resolution. But lowering the orbit, to get a closer view of the planet, is a one way ticket, eventually leading to MESSENGER’s impact on the surface of Mercury.

Mercury MESSENGER

The end will come sometime after March of 2015, on the far side of Mercury from our view.  MESSENGER will die alone, cut-off from us by distance and astronomical happenstance. In the words of MESSENGER PI, Sean Solomon, “This will happen in darkness, out of view of the Earth. A lonely spacecraft will meet its fate.”

This emotional attachment and personification of machines seems disingenuine to some people; spacecraft aren’t people, they are collections of wires and circuits and nuts and bolts — they don’t have souls to become attached to.  I dunno. I think they do have souls. They are the embodiment of every one who ever imagined them, worked on them, or stared at the data and pictures they returned. These little robots, in a way, are us. They are our dreams. Dreams of adventure, of knowledge, of a better tomorrow, of understanding who and what we are in a Cosmos that is vast and daunting.

And so today I smiled at the pale blue picture of our long departed friend, Voyager 1. And on the day it falls silent, I’ll shed a tear and drink a drink to its remarkable voyage, a voyage it made for you and me.