Several months ago, I wrote here about a fridge-sized space probe called Philae. The European Space Agency (ESA) flew her (well, why not “her"?) to and dropped her on a comet, 67P/Churyumov-Gerasimenko. No, this wasn’t your everyday Mangalore-Madurai flight. It took the best part of 10 years and plenty of intricate manoeuvres.

Scientists believe Comet 67P dates from the very beginning of the solar system. Once Philae landed there, she was supposed to start telling us what it is like, even drilling into its surface to analyse the composition of the ancient rock.

But things did not go quite to plan. Philae landed, but then bounced off and soared slowly along for another two hours. When she finally came to rest on the surface, she was leaning against the wall of a crater. This left her solar panels in shadow, unable to generate any electricity. So she ran out of power in just 60 hours and could no longer communicate with earth.

While not unexpected—the miracle would have been if Philae performed exactly as planned—this was still a huge disappointment to scientists, and to so many the world over who followed her descent onto 67P. How sad that she would now be forever silent.

But we should be careful with words like “forever". For after nearly seven mute months, Philae woke up last week. She didn’t say very much, just a “ping", but that was enough to know that she’s alive. That she might be able to resume her scientific purpose: telling us about 67P.

Remarkable, right? Well, even back in November, the ESA suggested that as 67P approached the sun, it was possible that Philae’s solar panels would catch some sunlight and supply her with electricity. This is what must have happened. And Philae must have been programmed to send a message home—ET phone home: but that headline is already taken, over and over again—as soon as she had the necessary power. Thus the “ping!" that warmed hearts the world over.

Though actually it’s rather more than a ping. Philae sent 85 seconds worth of data, hinting at much more to come.

Quite a story. But apart from everything else, consider for a moment the obstacles to communication like this. 67P is more than 500 million km from Earth. That means Philae’s data, travelling at the speed of light as it does—took better than 1600 seconds to reach Earth: nearly half an hour. It takes the same time to send Philae any kind of instructions.

WhatsApp that to someone.

* * *

And if a revived Philae isn’t enough for you, there’s recent news about another large rock flying through space, and another probe from Earth that’s looking at it. The probe, Dawn, launched in 2007. Dawn’s mission is to visit two objects, Vesta and Ceres, in the asteroid belt between Mars and Jupiter. Vesta and Ceres are considered “protoplanets". Like 67P, they can tell us about the very beginnings of the solar system.

Dawn orbited Vesta in 2011-12 before heading for Ceres, where he (well, why not “he"?) entered into orbit in March this year. He has already sent plenty of photographs of Ceres back to Earth. As you might expect, Ceres is pockmarked with craters big and small, meaning it has been bombarded by celestial debris since its birth—like our moon, and in fact like the earth itself. Some of the small craters even form long straight lines. There’s a nice explanation for that particular phenomenon that I’ll leave you to figure out for yourself.

But Dawn found another puzzle on Ceres that has baffled scientists. In the middle of one particularly large crater—about 90km across—there are two bright white spots. What could they be? Since March, as Dawn has moved ever closer to Ceres, we’ve got ever clearer images of these spots—to the extent that it seems that each is actually a collection of smaller white spots—but we still don’t know what they are.

Are they sheets of ice, reflecting light? Ceres has ice below its surface, this much we know. But how did it get above ground? Could a meteorite have smashed into Ceres and released some of the ice via a fissure?

Watching from the sidelines as I am, ice seems the most likely explanation. But with even a little thought, other possibilities come to mind. For example, it might be a large deposit of some mineral. Like salt. Or mica, which reflects light. Whatever it is, we’d still have to explain how it got there, why it is in that particular crater and no other, why one of the spots seems to be right at the centre of the crater.

Plenty to puzzle over. The good news is that starting later this month, Dawn will spiral down, closer to Ceres. In December, he will be in an orbit just 375km off the surface (compared to about 4,400km today). The images we get then may resolve this conundrum.

Or maybe not. Maybe we need a second Philae, this time to drop onto Ceres.

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners.

A Matter of Numbers will explore the joy of mathematics, with occasional forays into other sciences.

Comments are welcome at To read Dilip D’Souza’s previous columns, go to