Sunday, May 5, 2019

Asteroid Hunters by Carrie Nugent

This is an inspired little book with a lot of problems. I pulled it from the stacks at my city library neighborhood branch because I wanted something casual to read and because I wanted to find a book to review for my local astronomy club newsletter. Asteroid hunting is one of the activities of amateur astronomers that intersects the work of professionals. Comet hunting is another. I was pleasantly surprised by Dr. Nugent’s easy explanation of why, contrary to our common assumptions, asteroids and comets are often the same. That was one of several interesting facts in a flawed presentation. 

With a lot of hope, I expected to read about amateur and professional astronomers, including photographs of the instruments used by my unpaid colleagues who work for the love of it. Instead, I soon met the first of over 20 errors of fact. It started with the vernacular American style which includes jarring grammatical lapses and sentence fragments.
  • “When I tell people I’m a space scientist studying asteroids, they sometimes assume I’m a super-smart math whiz. The kind of person who skilled a bunch of grades and went to college when they were sixteen.” (page 2)
  • “There wasn’t going to be any surprises.” (page 15)
  • “Soy latte, check e-mail, wait for the caffeine to kick in.” (page 29)
  • “… there’s a few…” (page 73)

Nugent writes, “… sometimes artifacts of the telescope can masquerade as an asteroid moving across the sky. These artifacts can be a series of cosmic rays, or the edge of a flare from a bright star.” (page 29).That is not what an “artifact” is in a viewing instrument. When you see your eyelashes in a microscope because of internal reflections in the lens system, that is an artifact. 
Asteroid Hunters by Carrie Nugent, 
TED Books Simon & Schuster, 2017, 
108 pages, $16.99.
https://www.crnugent.com
Nugent wrongly claims that astronomers in 1800 thought that the planets orbit in circles. “Existing methods of the time [1800-1802] used the assumption that the planets traveled around the Sun in circular paths, when in reality they traveled on a specific geometric path called an ellipse.” (page 43) But it was Kepler who first fit the orbits of the planets into elliptical paths about 1605.

At that point, Nugent already referenced Kepler, though she never mentions Newton. Kepler showed that the planets travel in ellipses and then that was proved as mathematically necessary by Newton. Newton’s calculus demonstrated that objects moving under the influence of a central force do so in paths that are conic sections. It is called a “necessary fact” something that is both required by logic and observed in experience. The shape of the orbit (line, hyperbola, parabola, ellipse, circle) depends on the velocity of the object. 

An underlying theme of this book is that getting money to search for near-Earth asteroids has been difficult because the political agencies that fund such research consider the possibility of catastrophe to be remote. The kind of asteroid that could end life as we know it comes only every 65 million years. However, two asteroids dramatically became meteorites in recent times: the Sudan 2008 TC3; and Siberia 2012DA14 (Chelyabinsk). The Sudan fall was predicted a few hours ahead of impact. Siberia was a complete surprise.

Nugent explains the difficulties in spotting asteroids. For one thing, the Sun blocks our view. But she also explains the work-arounds of observation and orbit plotting. At least, she says that such tools exist.  In fact, Nugent presents orbit plotting as extremely complex, difficult mathematics that only a genius could master. If not for Carl Gauss, we would be working in the dark, so to speak. But it only takes three points, three observations, to define a conic section. 

That being so, what makes orbit plotting and asteroid hunting a challenge is the many perturbations that change the neat conic sections into wobbly, wonky drunk walks. Nonetheless, celestial bodies travel in very predictable, mathematically definable paths. Even the perturbations are knowable and predictable. That being so, it remains that even now, 300 years after Newton’s Principia, for the most exacting predictions, we depend on tables of previous observations, rather than applying undergraduate calculus to three observations.

Nugent says that “Space is cold.” (page 64 para 6). It is not cold if you are in direct sunlight. Then, it is hot. Whether space is hot or cold depends on the definitions. Statistical mechanics defines temperature by the number of particles with a significant velocity. If you have one or two traveling at the speed of light,  you have “cold.” If you have thousands going 10 mph, it is hot: just rub your hands together as fast as you can. (Don’t burn yourself.) 

Nugent discusses the important statistical method of her team without naming it. Writing about p-values, (page 76) she calls it “debiasing” (pgs-75-77). “They also knew the time and location in the sky of every image NEOWISE had ever taken. The computer simulation exactly modeled how NEOWISE observed the sky and what it would be able to see. Then, they simulated hundreds of thousands of ‘synthetic’ asteroids and ran them through the simulation to see how many asteroids NEOWISE would have seen. The result was compared to what NEOWISE actually saw.” Nugent then gives an example using 10, 12, and 18 samples.  “Of course, the actual implementation is more complicated than that, and many more asteroids are simulated so that the results have statistical significance. But you get the idea. With this method, we know what we don’t know.” (page 77).  

Dr. Nugent delivered her TED Talk in February 2016. This book came out in 2017. But p-values and “statistical significance” were being questioned for the very misuse and abuse of statistical methods by scientists such as Dr. Nugent. 
  • “Why Most Published Research Findings are False,” John P. A. Ioannidis, PLoS Medicine, August 2005. https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.0020124
  • “How to Use p-Values Correctly,” Kerry Grens, March 9, 2016,The Scientist. https://www.the-scientist.com/the-nutshell/how-to-use-p-values-correctly-33910
  • “The ASA’s statement on p-values: context, process, and purpose,” by Ronald L. Wasserman, and Nicole A. Lazar, The American Statistician, March 9, 2016. https://www.tandfonline.com/doi/full/10.1080/00031305.2016.1154108

It is a serious fact that keeping up with all of the sciences not related to your own is a challenge. However, this controversy was first opened for discussion in 2005 and just as Dr. Nugent was approaching TED Talks, it burst out. The ASA Statement can be found on many websites for university undergraduate classes in statistics. She should have known. They all should have, rather than surging forward with their millions of computer-simulated asteroids.

And yet, there is much here, even though the details may not motivate anyone else. I always accepted the easy statement that a thousand Earths could fit inside Jupiter. The giant planet’s diameter is about ten times our own’s. Ten cubed is a thousand. (In fact, it works out to Jupiter’s volume being about 1381 times that of Earth.) In a footnote, Dr. Nugent explains that packing spheres leaves space between them. Only about 800 Terras could be fit into Jove. I learned something that I should have figured out on my own. So, I am appreciative.

Jupiter is discussed in the context of asteroid Shoemaker-Levy 9 striking Jupiter. “Unfortunately, the impact was going to hit the side of Jupiter that was facing away from Earth, so astronomers with telescopes wouldn’t have a direct view. … A fleet of spacecraft was trained on Jupiter, including the Hubble Space Telescope, the ROSAT X-ray satellite, and …” (page 81) Neither of those was in any position to see the far side of Jupiter. Both Hubble and ROSAT orbited Earth. In fact, Hubble did send images from after the impact. 
This NASA Hubble Space Telescope image of Jupiter's cloudtops was taken at 5:32 EDT on July 16, 1994, shortly after the impact of the first fragment (A) of comet Shoemaker-Levy 9. A violet (410 nanometer) filter of the Wide Field Planetary Camera 2 was used to make the image 1.5 hours after the impact.  http://hubblesite.org/image/170
And it was not a single event but a series of impacts. The comet had broken up two years earlier in a previous pass-by in July 1992. The fragment stream impacted the planet over six days, July 16-22, 1994. As Jupiter rotates on its axis with a period of about 10 hours (9 hr 55 min 30 sec), the effects of the fall could still be detected. In fact, “ripples” on Jupiter out to its thin ring were recorded as late as 2002.  (See https://en.wikipedia.org/wiki/Comet_Shoemaker–Levy_9) and see https://www.skyandtelescope.com/astronomy-news/comet-shoemaker-levy-9-20-years-later-07162014/). So, the actual moments of these impacts may have been missed by all, but being in Earth orbit would not have made any difference.

When you watch Prof. Carrie Nugent’s TED Talk here, it is obvious that she is excited about her work and the opportunity to share it with an audience that will care. Those six minutes are fine as far as they go. The difference is that print captures everything except (perhaps) exuberance. 

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