Marianne J. Dyson

Review of You Are The First Kid on Mars

Reviewed by: Marianne Dyson, revised August 2009 (original June 2009)

I recently received a message from the author pointing out an error I made in my original review, and suggesting alternative ways of interpreting some of the science I criticized. I have thus revised the review below and adjusted the rating upward.

I apologize to Mr. O'Brien and to my readers for saying that Earth and Mars could not be as close as 35 million miles--they CAN, and actually were in 2003 (though it won't happen again for 60,000 years). My mistake came from stupidly having the figure of 50 million KILOMETERS in my head as the minimum distance, not miles. Duh. I should ALWAYS double check my units!

I also said that it was impossible to see a full Earth when departing for Mars. Mr. O'Brien reminded me of the "opposition" mission trajectory (discussed in Zubrin's book, Case for Mars) that swings toward the sun (when Earth could be seen as full) and then outward to Mars. I have not seen any recent materials suggesting this trajectory, but it was incorrect for me to say it was impossible. I have deleted that paragraph. I hope you all will forgive me for these errors.

This "exercise" has driven home a significant point to me, for which I must thank Mr. O'Brien. Errors are all too easy to make, whether caused by simple typos, a lack of familiarity with the science, or too-narrow an interpretation of it. No one person can find and correct them all, or make sure that the information is clear to everyone who reads it. We all have misconceptions in our heads.

I started reviewing books for their accuracy because I hoped to help weed out some of the worst offenders, warn librarians about the mistakes, and encourage publishers to use fact-checkers. But it seems that mostly what I've accomplished is upsetting some fine authors (and their editors) who are in positions to actually make a difference in science literacy.

So, I've rewritten my review of O'Brien's book, and though I still find some of the science questionable, and at least one "fact" completely wrong, I hope that the review below is more balanced in giving credit where credit is due and will be more useful to librarians and parents.

The book opens with, “Would you like to go to Mars?” My experience asking this very question of tens of thousands of children at school visits has shown that prior to being given reasons to go, about 80 percent of children will answer “No.” (Try it yourself.) But assuming the reader decides to continue, the next page declares, “Mars is a cold place. A dusty, rocky, windy place.” This is not a very appealing first introduction to Mars, but then again, some places in the American West could be described this way, too--and people found them beautiful and valuable, nevertheless. I hope that children will view Mars this way, too.

The actual trip begins with a ride on a space elevator--a cool idea that, though unlikely to happen in my lifetime, is a good choice for introducing the idea that there are alternative ways to reach space than on a chemical rocket. The illustration of the boy holding his helmet and heading toward the elevator is absolutely gorgeous. I said this in my original, and perhaps I should emphasize it more--the illustrations in this book are absolutely gorgeous!

In my original review, I noted that on page 5 it says, “There is no gravity in space, so you float through the air, lighter than a feather.” My response, "No, and again, NO! There absolutely IS gravity in space. Usually, people are weightless in space because they are in freefall. (See my book, Space Station Science.)"

The author wrote to me that he used the words, "no gravity in space" casually, because the character does not feel gravity. I wish he had said that instead--that he didn't feel gravity, or simply said he was weightless. He argues that "freefall" is too difficult a concept for young children--perhaps. But then, so is the true nature of gravity! And saying that you float "through the air" is also misleading. No air is required to float in space. Children might think that people float on air like things float on water--and that is NOT the reason people float in space. I suggest that no explanation is better than a wrong or misleading one.

However, the author can certainly be forgiven for adopting this phrasing which is unfortunately used regularly by astronauts and NASA scientists. This usage of "zero g" and "there is no gravity in space" is so widespread that probably 95 percent of children and their teachers and members of the public believe that there is no gravity in space.

Undoing this misconception is a passion of mine, and though it may be a lost cause, I hope Mr. O'Brien will forgive my strong reaction. I really don't blame him--I blame my friends in NASA whom I hope get so tired of hearing me harp about this that they will start using freefall instead!

The next main science topic in the book is the use of a space elevator. When riding a space elevator, your weight gradually decreases as you get farther from the Earth’s center. [The force of gravity equals a constant times the masses of the attracting bodies divided by the distance between their centers squared.] Your weight would be near zero only as you passed through the center of mass of the elevator and Earth. (To stay over one place on Earth, the elevator must be anchored near the equator and extend so the center of mass is near geosynchronous orbit [GEO].) After passing through this point, weight would return as a result of “artificial gravity” also known as centripetal force.

Think of a space elevator as a bead on a string with a stone on the end. As you whirl it around, the bead moves outward. A ship “jumping off” at the end of the elevator would be flung away from Earth as if someone cut the string. [Ref: http://chaos.swarthmore.edu/courses/PDG07/AJP/AJP000125.pdf, accessed 6-17-09] (If they cut the string below GEO, the bead would fall back to the ground—it is not going fast enough.) It depends on the height of the elevator and mass of any counterweight, so I don’t know what acceleration would be felt at a station on the end of the line, but it would not be zero.

The author wrote to me that he intended his station to be near GEO, and that is why the boy is weightless. He said my original criticism of the boy being in freefall is therefore invalid, and given that assumption, he is right.

But getting off a space elevator at GEO if your destination is Mars does not make sense to me. The main advantage of space elevators is to avoid using fuel to reach the speed necessary to reach your destination. I asked some other scientists if they knew of a reason to get off at GEO if you were destined for Mars--and found at least one: to do assembly without having to deal with centripetal force. There is no assembly in this particular book, and I still think that is an unlikely scenario, but it is not impossible--and we've all seen how politics can saddle us with orbital choices that may not be optimum. So, okay, the kid can be weightless--but not because there isn't any gravity!

Once the ship exits the elevator, the passengers would be freefalling around the sun, and would float. The illustrations show the people sitting and standing inside the ship as if it has (artificial) gravity. Though no mention is made of it spinning, the author pointed out in his message that the illustration shows a ship that could rotate. He makes a good point, so I have deleted my comments about that.

To reach Mars, the speed required is generally in the range of 40,000 mph. [Ref: http://members.cox.net/jhaldenwang/mars.htm, accessed 6-17-09] The book says “The launch is slow and smooth, and gradually the rocket builds up speed until it is going more than 75,000 miles per hour.” A higher speed would have the advantage of shortening the trip—so though I think this acceleration should come from using the space elevator instead, it is okay to have the ship add speed. If it really is departing from GEO, it is absolutely necessary to accelerate.

It says on page 8 that the "rocket to Mars travels when the planets are closest together." This is only partially true. A typical mission would depart when the two planets are farthest apart so that it arrives when they are closest together. I mention this because children may be left with a misconception about how orbits work--that somehow, a ship just scoots across this minimum distance when it is more like matching speeds on a race track. The trip continues towards Mars. [Deleted statement about seeing full Earth. Unlikely, but not impossible.]

The ship docks in orbit around Mars, and then a lander takes the child to the surface. I originally criticised the illustration of the departing rocket as being exactly backwards relative to the orientation it should be upon entering the Martian atmosphere, saying the engines should fire into the direction of flight to slow it down. The author disputes this statement, saying the rocket is using engines to maneuver, a heat shield protects it, and parachutes slow it down. He says that current Martian spacecraft have used this design.

Perhaps I should have given him more artistic license--and assumed he just left out some parts of the entry? A ship arriving at Mars must be slowed down a lot, via aerobraking if there is time, or via engines firing into the direction of flight if not. Once the ship has slowed, it must be protected from friction with the atmosphere during entry. That requires a heat shield. This shield for Apollo was ablative, it burned off. The shuttle uses fragile carbon tiles--and it was their failure that caused the loss of Columbia. The current Mars rovers used ejectable heat shields. The illustration does not show any of these. So my criticism remains, though I don't consider this a very serious problem--just an omission of an important part of the entry sequence.

The text notes that you need a spacesuit on the surface, which I noted in my orignal review is correct, but then I said it was not to keep you warm, but to keep you cool. The author objected that a spacesuit does keep you warm--because without it, you would indeed freeze. He is right, and I should not have been so critical of such a minor point. However, because so many authors have emphasized this as the main purpose of a spacesuit, there is a growing misconception about how space suits work. If you have ever worked up a sweat inside a plastic raincoat, you know that the body produces plenty of heat, in fact too much—suits must provide cooling, not heat. But it is cold in space, and an astronaut's hands and feet sometimes need to be warmed. So, okay, the text about space suits is fine. I should also note that the author says first and foremost that a suit provides breathable air--and that (pressure) is indeed it's primary purpose.

The habitats and activities on the surface are realistic, and beautifully illustrated. I especially liked the sections on what life might be found. The robots doing various chores should also have strong kid appeal.

On page 26, it says “There’s a huge mountain up ahead.” Though it is true that Olympus Mons is three times taller than Mt. Everest, with a base as large as the state of Arizona, the slope is so gradual, that even from an airplane, you couldn’t see it as a mountain. The author took some artistic license here, and though I understand that, I would still prefer that children be shown the reality and not given a misconception. Likewise, Valles Marineris is so wide that only one side would be visible at a time, though there should be a few places where both sides of tributary canyons are visible. The author said that is in fact what he illustrated, but I think he could have said so to avoid another misconception.

The “More About Mars” pages at the back contains a glaring error that the author admits is embarrassing, and thankfully, will be corrected in any future editions. It says, “Mars is the closest planet to Earth.” Venus at closest approach is about half as far away as Mars.

The second “fact” says the distances of Earth and Mars are 90 and 140 million miles respectively. These rounded-off numbers are close enough for a children’s book. I apologize again for associating the wrong units in my muddled brain and saying that the two worlds could not be as close as 35 million miles. A bright child might wonder why subtracting 90 from 140 is 50 versus 35, the stated and correct minimum distance listed in the next fact. Tell them that 90 and 140 are AVERAGE distances, and thus 50 million miles is the average minimum distance, and 90 plus 140 (230 versus the correct 228 listed) is the average maximum distance apart.

As for how long it would take to get there at highway speed, I checked this number assuming 60 mph for 24 hours for 365 days, and got 525,600 miles-- times 60 years is 31 million miles. That is less than the minimum distance. The author says he used a higher speed, and that gives a closer answer, but why not compute it using the average distance and come up with a more realistic time? Besides, the actual distance traveled is more like 400 million miles for a typical Hohman transfer. I think the intent here is to use time as a measure of distance because it is, of course, not even possible to leave the surface of Earth without going thousands of miles per hour.

I noted in my original review that Mars is not colder simply because it is farther from the sun, as stated in the text. Consider that Venus is hotter than Mercury, and you will know that an atmosphere is also a primary factor in surface temperature. The author says that yes, there are other factors, but what he says is still true--if we put Earth at Mars' distance, it would be colder. I agree. I mentioned this for those parents who like to ask their kids questions like, "Why do you think Venus is hotter than Mercury yet Mars is colder than Earth?" I don't think the text needs to be changed, and apologize if these type of comments come across as negative.

In summary, You Are the First Kid on Mars falls short in the accuracy department mostly because the science community continues to use bad terminology that authors naturally mimic, and also because the book includes a very complicated new concept that is not well understood: a space elevator. I originally gave this book 2 points (one for illustrations, and one for a new idea). Considering the topic and the difficulty of explaining it to young children, and that I probably overreacted because of the "no gravity" issue, I am adding two points (one for readability, and one for science in the plot). Total: 4 points. This book is beautiful and creative, and as long as parents and teachers inform children that there IS gravity in space, then it is okay by me.

Title: You Are The First Kid on Mars
Author: Patrick O'Brien
Ages: 4-8
Number of Pages: 32
Format: hb
Publisher: Putnam Juvenile
Pub Date: 2009
Retail Price: $16.99
ISBN: 0399246347

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