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May 2019

Reading Astronomy News: This Interstellar Asteroid is Accelerating


By Stacy Palen

As I was working on the first draft of Chapter 3 for the fourth edition of Understanding Our Universe, I ran across this wonderful summary article about ‘Oumuamua by Steven Spence of GotScience Magazine. You probably remember that ‘Oumuamua is the first interstellar object that we’ve observed in our Solar System. This article compactly lays out the case for how we know it comes from another star, how fast it’s moving, and why its acceleration as it leaves the Solar System is “weird." It’s practically chapter 3 in a nutshell! 

To read This Interstellar Asteroid, by Steven Spence, click here.

  1. In the discussion of where ‘Oumuamua came from, the author states that it is “moving on an open hyperbolic trajectory.” Make a sketch of what such a trajectory would look like. How is it different than a path followed by an orbiting object?

    Answer: They should draw a hyperbola; many will have to look this up. A hyperbola is not closed, like an ellipse is closed.

  2.  ‘Oumuamua’s trajectory is described as having an eccentricity of 1.23. But the maximum eccentricity for an ellipse is 1.00. What is the resolution of this apparent contradiction?

    Answer: Only objects that are orbiting, and bound to the system by gravity, travel on ellipses. Objects that are unbound can travel on trajectories that don’t meet the requirements for an ellipse.

  3. In the article, ‘Oumuamua’s speed is described as fast enough to cover the distance from Earth to the Moon in 73 minutes. The New Horizons space craft covered the same distance in 8 hours. Approximately how many times faster is ‘Oumuamua traveling than New Horizons?

    Answer: In “cowboy” math, 73 minutes is about an hour. So ‘Oumuamua must be traveling about 8 times faster than New Horizons, to cover the same distance in an 8th of the time.

  4. ‘Oumuamua reached the orbit of Jupiter about an hour earlier than expected. Why does this imply that the object has accelerated?

    Answer: In order to cover the distance in less time than expected, the object must be traveling faster than expected. This means there must be an unexpected increase, or less-than-expected decrease, in the speed of the object.

  5. The best idea, currently, for how ‘Oumuamua is accelerating is that it is “comet-like outgassing.” Outgassing occurs when a jet of gas shoots out from the object. Use Newton’s third law to explain how an object “outgassing” can cause an object like ‘Oumuamua to accelerate.

    Answer: This is exactly how a rocket accelerates! Because it is a closed system, if some of the mass accelerates in one direction, there must have been a force that pushed that mass. By Newton’s third law, there must be an equal and opposite force pushing the rest of the mass in the opposite direction.




Reading Astronomy News: Earth’s Magnetic Field On The Move

Earth's Magnetic field
Image Credit: Emmanuel Masongsong/UCLA EPSS/NASA

By Stacy Palen

In January, geologists updated the model of Earth’s magnetic field, a year ahead of schedule.


1. Study the map titled “Magnetic Motion.” How much time separates each pair of red dots between 1900 and 2010?

Answer: The dots indicate 10-year time intervals until 2010. There is an extra dot placed for 2015.


2. In general, how does the movement of the magnetic pole since 1990 compare to the movement of the pole prior to that time?

Answer: Because the red dots are much farther apart after 1990, we can conclude that the pole is moving a lot faster in the last few decades than it did prior to that.


3. Why do we care about what happens to the magnetic pole of Earth?

Answer: The position of the magnetic pole underlies all navigation. If we don’t know where the pole is, we don’t know where we are.


4. Why did geologists decide to update the model a year earlier than expected?

Answer: Because the position of the pole was changing so fast that navigation was becoming inaccurate.


5. What is the working hypothesis for why the position of the magnetic pole is changing so rapidly right now?

Answer: A jet of liquid iron is weakening the magnetic field in Canada. This means that a second patch of magnetic field in Siberia is relatively stronger, so the pole is moving in that direction.


6. How does this news article relate to what you have learned about Earth’s magnetic field?

Answer: We have learned that Earth’s magnetic field changes over time, and that the history of those changes are recorded in rocks. We have also learned that the magnetic field affects the aurorae in Earth’s atmosphere. As the magnetic field changes, this should affect the aurorae as well.