Today, the Cassini spacecraft is scheduled to make its closest approach ever to the Saturnian moon Enceladus. Flying to within 50 km of the surface, Cassini hopes to probe the chemical makeup of the geysers spewing from the south pole of Enceladus. Previous investigations indicate the high probability of an ocean beneath the crust of Enceladus, and this latest investigation will seek the tell-tale signs of chemistry that might indicate the presence of life.

Here are some links that explain further:


Mars News

This week NASA announced that it has discovered evidence that liquid water is flowing on Mars.  Not just in the past as previously announced, but now.

The existence of liquid water on the surface of Mars is rather unexpected. To understand why, look at the following phase diagram chart, showing the states of water as a function of pressure (vertical axis) and temperature (horizontal axis):


On the surface of the Earth, we live at 1 atm. This means that water exists as a solid (“ice”) at a temperature below 0 degrees Celsius, as a liquid (“water”) between 0 and 100 degrees Celsius, and as a gas (“water vapor”) above 100 degrees Celsius. You can see this in the diagram above by following the horizontal dotted line from left to right at P = 1 atm.

Let’s look at Mars.  The atmospheric pressure on the surface of Mars is about 0.006 atm. Look at the chart above.  At an atmospheric pressure of 0.006 atm, liquid water is just on the knife-edge of being able to exist at all. If the pressure were slightly lower than 0.006 atm, water would transition directly from a solid to a gas with an increase in temperature. (An example with which you’re familiar on Earth is carbon dioxide, which transitions directly from a solid  we call “dry ice” to a gas at 1 atm). Slightly higher, liquid water could exist, but only in a very narrow band of temperatures.

Atmospheric pressure and temperatures make the existence of liquid water on Mars an extreme challenge.  At the very least, the above phase diagram shows why finding liquid water on the surface of Mars is very surprising.  Perhaps minerals and salts dissolved in the water shift the phase diagram enough to permit liquid water to exist under a broader range of temperatures. It is certainly worth exploring further, in person.

Speaking of exploring in person, Eric Berger (@chronsciguy) of the Houston Chronicle wrote an article about why it is so hard to get to Mars. Definitely worth reading.

Mars News

August Volatility in the US Stock Market


Driving home the other day, I heard a segment on NPR that was discussing the recent market downturn and its possible causes. Interestingly enough, one of the guests during the segment asserted the following:

“Firstly, the markets are very thin right now because it is August and you have a lot of the seasoned traders away on vacation. You’ve got less volume than anywhere in the markets. And so there’s a long tradition of people overreacting during this vacation season.”

When pressed on this point, the guest analyst didn’t waiver:

“But the reality is that, you know, many of the most seasoned and senior traders tend to go on vacation this time of year. And yes, we can all remain in contact with our iPhones and our iPads and whatever else while we’re on the beaches. But traditionally, you have had a lot of pretty wild market movements in the month of August historically.”

The question of volatility seems to be an easy point to test. First, some assumptions:

  • A market index such as the S&P 500 is an indicator of the broader market performance.
  • Volatility is high if the closing price on a given day is markedly different (up or down) than the closing price on the day prior.
  • A given month is more volatile if it has more high-volatility days than another month.

Based on the assertion that August volatility is caused by junior traders, I infer that with senior traders in charge, there should be less volatility. Otherwise, I claim that the causal relationship between volatility and the seniority of the traders is not provable.

To test the theory, I downloaded the S&P 500 closing prices for the last 10 years and performed some calculations. First, for each day I calculated the change in closing price, and percentage change in closing price. Here is an example:


S&P 500 Closing Price

Change from Previous Day
C(i) = P(i)-P(i-1)

Percentage Change from Previous Day
R(i) = C(i)/P(i-1)



















The variations in the percentage change in closing price, calculated by finding the standard deviation, will provide the measure of market volatility in accordance with the assumptions above.

Using the S&P 500 closing prices for the last 10 years, performing the above calculations, segregating the data into 12 separate monthly bins, and calculating the standard deviations for each monthly bin yields the following:

 Month Standard Deviation Rank
Jan 0.0114 7
Feb 0.0109 8
Mar 0.0128 5
Apr 0.0096 12
May 0.0105 10
Jun 0.0109 9
Jul 0.0100 11
Aug 0.0136 4
Sep 0.0141 3
Oct 0.0191 1
Nov 0.0168 2
Dec 0.0122 6

Based on the daily variations in the S&P 500 closing prices over the last 10 years, it is true that August is one of the more volatile months. However, the variations in August are exceeded by the Fall months – September (#3), November (#2), and October (#1). Therefore, if the “junior varsity” traders being in charge cause volatility in August, what is the explanation for the even higher volatility in the Fall months?

Perhaps the guest analyst had some other measure of volatility in mind – inter-day swings in prices, daily trading volume, or something else I haven’t considered. Based on the volatility in daily closing prices, however, August is in the top half of volatile months, but isn’t as volatile as the Fall months. Therefore, I question the association of August volatility with junior traders. Based on data over the last 10 years, it doesn’t seem to be a viable explanation based on the assumptions above.


Is The Stock Market Volatility A Correction Or A Full-Blown Crisis? August 25, 2015

S&P 500 Historical Data, last updated 2015-08-26 6:51 PM CDT

Image via pixabay.com

August Volatility in the US Stock Market

2, 4, 8


A few weeks ago I ran across a very simple puzzle. It is a rule based on a sequence of three numbers. Some sequences obey the rule – and some do not. The challenge is to guess what the rule is. According to the opening paragraph of the article accompanying the test, the test sheds light on government policy, corporate America and why no one likes to be wrong.

The puzzle starts with the following:

2, 4, 8 – obey the rule.

Then it is up to you to provide other sequences and guess the rule.

Here is the link:


Go ahead.

Give it a try.

I won’t spoil it for you.

Once you’ve given it a try, return here.

I’ll wait.

(Jeopardy music.)

What did you think? Did you guess correctly?

The test explores confirmation bias. Were you willing to search for a “No” answer, or did your couch your guesses to give “Yes” answers? In my case, I started with a specific sequence that gave “Yes’s”: A x B = C, and tried a few others that all led to “Yes” as well.

I wondered: are there any sequences that give “No?”  So, I took a stab until I got a “No.”

The first “No” answer taught me more than all the “Yes’s” I got before. I kept trying to get “No’s.” In the end, I got 5 “Yes’s” and 7 “No’s”, at which time I decided upon an answer: each number in the sequence is greater than the number before it.

The first lesson I took away is that this test applies to more problems than those dealing with numbers.   The basic principle is applicable to many situations we face every day. In the weeks following the test, when I faced a situation and thought I knew the answer, I said to myself, “2, 4, 8.” It’s my self-cue to ask another question.

Another key takeaway: the best questions are those in which I get the opposite of what I was expecting. Such an answer shakes up confirmation bias and tells me something new.

2, 4, 8 – a simple yet powerful test to challenge confirmation bias.

2, 4, 8

Space Can Be Unforgiving


After a string of successes, SpaceX encountered a setback with the failure of SpaceX CRS-7 mission yesterday. For cargo services to the International Space Station, it has been a somewhat unlucky string of missions. First, the Orbital Sciences Corporation Orb-3 cargo mission failed in October 2014, followed by the Russian Progress M-27M in April 2015. This makes three in the last year.

Regarding the SpaceX CRS-7 mission, here are a few links that cover the failure:

  • Marcia Smith of the excellent SpacePolicyOnline.com provides a write-up on the preliminary cause of the CRS-7 failure.
  • Here is NPR ‘s coverage of the failure.
  • Lastly, here is NASASpaceflight.com’s detailed write-up on the failure.
Space Can Be Unforgiving

Poking at US Space Policy

Dr. Paul Spudis published two articles in recent days that caught my attention. The first discusses a proposed Chinese mission to the far side of the Moon, and the second discusses the search for life on Mars.

In total, the two are a continuing theme of questioning US space policy, and are a good read. Looking at both in a big-picture sense, one has to wonder why the US is choosing to pass up on developing cislunar space, treating it as nothing more than a proving ground for developing an eventual mission to Mars.

Food for thought.

Poking at US Space Policy

HST at 25

Space enthusiasts everywhere are celebrating the 25th anniversary of the Hubble Space Telescope. And it is with good reason. On this day that marks the 25th anniversary of the landing of Shuttle mission STS-31 that delivered HST to orbit, I wish to share a few thoughts and links that make this anniversary special to me.

A few years ago I reflected on how each of the Shuttle missions associated with HST served as a “signpost” to various stages of my career at NASA.  Those words from the past are just as relevant today.

Reflections of Hubble

Another retrospective is via an interview with Bill Reeves, who served as the Lead Flight Director for Shuttle mission STS-31 that delivered HST to orbit. I had the pleasure of working with Bill in later years before he retired, and his words of reflection on HST illustrate the deeply insightful person that he was at that time, and still is today.

Earthquakes and Compassion: Houston Matters (Bill’s retrospective is from 16:10 to 25:00)

Once Hubble was on orbit, we all knew what happened. Its vision was blurry. The next link recounts the race to save Hubble and its reputation, via an interview with Ed Weiler, who was Hubble Chief Scientist at the time. I later met Ed on two occasions – the first when he was the Associate Administrator of the Office of Space Science at NASA Headquarters, and later when he was the Director of the Goddard Space Flight Center. He’s an interesting fellow with interesting views, some of which are hinted at in this story.

Fixing Hubble’s blurry vision

Perhaps the greatest success of Hubble goes beyond the telescope itself. In one way, HST is the perfect example of the blending of art and science. It is the powerful, insightful images from a scientific standpoint coupled with astonishing beauty that strikes a chord with me. Here are some of HST’s most incredible images.

15 Magnificent Images from the Hubble Telescope

Lastly, in looking outward, HST permits us to look inward. The images of astronauts servicing Hubble on several occasions demonstrate how NASA’s scientific and human endeavors can work together. Beyond that, Hubble has allowed us to learn our place in the universe. For me, the next story brings this to life.

Hubble Telescope Celebrates 25 Years In Space

And so, on this 25th anniversary, I salute the Hubble Space Telescope once again for being a special part of my space life, and the space life of the rest of us. Cheers!

Oh, and wait until you see what’s next

HST at 25