Alan Stahler: Local launch to Mars |

Alan Stahler: Local launch to Mars

Alan Stahler

The "evening star," shining bright in the west after sunset, is not a star at all, but planet Venus. Venus will grow brighter, all through summer and into the fall — I'll write about Venus in the future.

Not as bright as Venus, but growing brighter all the time, is ruddy-red Mars. Mars will be easy to spot, early Sunday morning, as the moon sidles up to it in the pre-dawn sky. But you might want to look for Mars, not quite so close to the moon, before dawn on Saturday.

The best time to send a spacecraft to Mars is when Mars is closest to us — saves time, saves fuel. With Mars approaching the part of its orbit closest to the sun, and Earth approaching the part of its orbit between Mars and the sun, the time to launch is now.

The InSight mission is scheduled to launch toward Mars, this Saturday, before dawn.

This will be the first launch of an interplanetary spacecraft from California, and the rocket's exhaust, over southern California, will likely be visible here in the north.

Imagine there's a gift-box waiting for you on the shelf. You'd love to know what's in it, but the card on the box says, "Do not open until … " … until months from now. What could be in it?

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You heft the box, to see what it weighs.

You shake the box, and listen for something rattling.

Earth's core lies thousands of miles beneath our feet. It would be cool to know what's down there, but the core is covered — mantled — by thousands of miles of rock.

We could try to drill down, but the deepest hole we've drilled so far descends barely seven miles. That leaves thousands yet to go. What to do?

Think of the Earth as a gift. We can heft the Earth — not pick it up, but measure the pull of its gravity, on us, on our surroundings, on the moon.

From this we learn that our core must be denser — much denser — than the rock here at the surface. Earth's core is made of iron, most likely.

Shaking things up

We can shake the planet — in a small way, with dynamite, TNT, nukes. But to really shake things up, we again depend on nature: Earthquakes.

You can grab the end of a rope and shake it, sending waves down its length. But you cannot grab water and shake it — water slips through your fingers. Water, therefore, cannot carry those ropy sorts of waves.

Earthquakes generate all sorts of waves, including ropy ones. We detect ropy waves whenever there's an earthquake in, say, Mexico. But we cannot detect those sorts of waves from earthquakes on the opposite side of the world — apparently, they can't get through Earth's core. We conclude, thereby, that Earth's core is liquid.

How did Earth evolve, from a humongous cloud of gas and dust, into a solid planet with a liquid core, a home for life?

The science of geology has expanded, in recent decades, into planetology. Comparing Earth with other planets yields information beyond what can be gleaned from looking at Earth by itself.

Mars is a giftie, which the InSight spacecraft will investigate by listening for, not earthquakes, but marsquakes … by measuring how heat flows through its rocks … by measuring how it responds to the sun's gravitational pull.

InSight's launch window opens at 4:05 a.m. Saturday. It will lift off from Vandenberg Air Force Base, the west coast's spaceport — look south. (If Saturday's launch is scrubbed, check the internet for the new date and time.)

And be sure to look, not far from the moon, for where InSight will land: the red-orange planet Mars.

Al Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at