What’s in the sky: Mars lander, a comet, a meteor shower

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Thursday, Dec 13, 2018 2:30 PM Updated Thursday, Dec. 13, 2018 3:38 PM

This composite image made available by NASA on Dec. 11 shows the InSight lander on the surface of Mars. The InSight lander used the camera on its long robotic arm to snap a series of pictures assembled into a selfie.

NASA/JPL-Caltech

Greetings, Stargazers.

NASA’s Mars InSight lander is designed to study the interior of Mars. InSight stands for interior exploration using seismic investigations, geodesy and heat transport.

It recently made a successful landing on the red planet, but the apparent ease with which the landing succeeded is rather misleading. Historically, touching down safely on the surface of Mars has been quite a challenge, and many landing attempts have failed.

The atmosphere is thick enough to burn up a spacecraft, but too thin to slow it down effectively. Combinations of heat shields, supersonic parachutes, thrusters, tethers and air bags have been used on various missions, and we should all be proud of this team’s accomplishment.

The period of Mars’ orbit is 1.88 years, so approximately every other year, we get a good look at Mars and have an opportunity to send a spacecraft there. If the cost of extra fuel were not an issue, we could fly there at any time. However, fuel is mass and launching more mass significantly increases the overall cost of the mission, as the initial launch from Earth is one of the most expensive parts of spaceflight.

The low-fuel option for getting to Mars uses orbital mechanics. All orbits, including Earth’s orbit around the sun, are elliptical so have a low point, called perihelion, and a high point, called aphelion.

But many orbits, like Earth’s, are very close to being circular. A circle is just a special kind of ellipse in the same way that a square is just a special kind of rectangle. By strategically firing your rocket once to get away from Earth, you just enter a new very elliptical orbit around the sun with the perihelion near the Earth’s orbit, and the aphelion near Mars’ orbit.

In this new orbit, the spacecraft can coast all the way from the low point near Earth to the high point near Mars. If the launch is timed correctly, the spacecraft will reach its new aphelion right when Mars is passing by in its orbit. Firing the rocket a second time changes the spacecraft orbit around the sun to match the orbit of Mars.

Then comes the really challenging part of the mission – landing safely.

This month

Mars is still the brightest thing in the evening southern sky. Venus has been spectacularly bright in the morning before dawn. If you get up then, you can’t miss it in the eastern sky.

The meteor shower for December is the Geminids. Sometimes as good as the summer Perseids, the Geminids should peak on the morning of the Dec. 13 or Dec. 14 and could have a rate over 100 per hour. It is best to look after the moon sets, which will be close to midnight those nights. Before my next column comes out, the Quadrantid meteor shower in early January is another of the year’s best.

There is a comet that might be visible to the naked eye in December. Comet 46P/Wirtanen should be the brightest comet in about five years if it reaches magnitude 3. This comet has an orbital period of 5.4 years, so is a regular visitor to the inner solar system. However, it doesn’t always pass close to Earth. Perihelion, the closest approach to the sun, is on Dec. 12, and the closest approach to the Earth is on Dec. 16, when it will be positioned in the sky near the Pleiades. It will be moving quite a bit across the sky from night to night, so use a chart to help find it.

Mesa Verde National Park is having its annual Luminaria Holiday Open House on Dec. 13. The plan is to have some telescopes set up for stargazing, so if you can participate or bring a telescope, let someone with the Four Corners Stargazers group know.

Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.