Showing posts with label Science. Show all posts
Showing posts with label Science. Show all posts

Tuesday, December 13, 2016

Habitable Planets around White Dwarfs

The white dwarf G29-38 (NASA)
The white dwarf G29-38 (NASA)
Out of all the odd scenarios that might be possible in our Universe, the thought that there might be habitable planets around White Dwarfs is one of the stranger ideas, in my opinion.  Imagine what it would be like to look up to see a White Dwarf dominating the daytime sky.  How close would the planet have to be to the star to receive enough light and energy to support life?  How would a planet find itself within the Habitable Zone around a White Dwarf?

This last question is particularly interesting because White Dwarfs are the remains of a Red Giants.  Red Giants are the last phase of fusion based main sequence stars.  Between White Dwarf, Red Giant and main sequence phases, a star changes so drastically that it is unlikely planets close to the star would survive into the next phase.  Some very interesting things need to happen for a planet to form within the Habitable Zone of a White Dwarf.

With main sequence stars, the Habitable Zone slows moves away from the star because the star slowly gets hotter.  A planet that starts out within the Habitable Zone of a young main sequence stars may not remain within the Habitable Zone for the full length of that star's life-cycle.[001] [002] Oddly enough, White Dwarfs have the exact opposite problem.  White Dwarfs cool down as they age.[003]  Habitable Zones around White Dwarfs will shrink until being too small for any sizable planet to exist within it.

The Habitable Zone around a White Dwarf is very small compared to that of Sun.  The Habitable Zone around Sun is roughly between the orbits of Venus and Mars.  The Habitable Zone around a White Dwarf is much closer than even the orbit of Mercury around Sun.[003]  It seems a planet that close to a White Dwarf cannot exist without some special events.

How do planets get to the Habitable Zone?

A planet could have existed in the previous solar system during the main sequence star phase, but much further out; so far out that it may not have been previously habitable.  When the main sequence star expands to become a Red Giant, then explodes to leave a White Dwarf, the planet would have to move from the outer reaches of the solar system to a stable close orbit.  This sounds incredible, but apparently it is possible since planets have been discovered around Neutron Stars, which go thru even more violence.[003]

Another possible scenario is it the matter ejected from the exploding Red Giant, or other remaining debris within the solar system somehow creates a new accretion disk around the newly formed White Dwarf, from which new planets could form.[003]
Water Cycle
Water Cycle

Even if either of these scenarios do happen, a water related challenge presents itself.  A lot water must somehow remain or be (re)introduced on these special planets.  Water is likely stripped from any existing planet that moves so close to the White Dwarf.[004]  Water is also unlikely to be available on any planet that forms so close to any star, White Dwarf or otherwise.  Maybe these planets could gather new water via the same processes as Earth, possibly "delivered to by a barrage of comets."[003]

If a planet is lucky enough to form around a White Dwarf, what's that White Dwarf going to look like in the sky?  White Dwarfs have a lot of mass, but they are very small in size.  White Dwarfs are about the same size as Earth.[005]  By my rough calculations, the Habitable Zone around a White Dwarf is about 5 times the distance of Earth to the Moon.  So, I image the White Dwarf would appear several times smaller in the sky as the Earth appears to the Moon.  Maintaining habitability of planet around a White Dwarf might be a bit like trying to keep warm outside on a freezing night next to a slowly fading campfire.

Primary reference:
A Loeb, D Maoz, Monthly Notices of the Royal Astronomical Society: Letters, Volume 432, Issue 1, p.11-15, arXiv:1301.4994 [astro-ph.EP], Detecting bio-markers in habitable-zone earths transiting white dwarfs

Monday, December 05, 2016

Small stars may have stable Habitable Zones, but habitable planets might not be common there

Protoplanetary accretion disk around a new star
Protoplanetary accretion disk around a new star
The previous article Limited lifespan of Habitable Zones around other stars (September 2016) covered the topic of Habitable Zones for planets around other solar systems.  However, Habitable Zones are only one of considerations for finding other stars with habitable planets.  Given the lack of data right now, sometimes science has to fall back on simulations.  These simulations do not replace actual observations.  Instead, they offer clues as to how we may be proceed in our search for hard data.

Habitable Zones appear to be more stable and longer lasting around small stars, such as Red Dwarfs.[001]  However, what are the chances of habitable planets appearing in these small zones around these small stars?  It turns out that the chances may not be good.

According to the study A Decreased Probability Of Habitable Planet Formation Around Low-Mass Stars, multiple simulations suggest that low-mass stars are unlikely to have terrestrial planets of sufficient size within their Habitable Zones.  This is due to a several factors.  That's not to say it is impossible nor improbable; just not as common as previous thought.[002]

Other factors

Besides Habitable Zones, another factor to consider is the Habitable Planet Mass Limit.  There is evidence that suggests that plate tectonic activity on a global level is a necessary factor for supporting life on a planet similar to Earth.  Planets must be of a particular size in order to allow for global tectonics.[002]  The lack or presence of global tectonics seems to be a factor in the differences between Venus and Earth.  Though Venus seems to be large enough, its surface heals too quickly to allow for global tectonics.[003]   The examples within our own solar system suggest that even when planets are large enough, there is no guarantee they will have global tectonics.

Another factor is the Protoplanetary Disk.  During the planet formation phase (accretion), there has to be enough material within the disk of matter that forms around very young stars (Protoplanetary Disk) in order produce larger planets.  Though there are a lot of unknowns regarding this factor, the "ratio of disk mass to stellar mass is roughly constant with stellar mass".  Also, planets seem to form much faster around small stars for various reasons.  With less time to form and less mass within the Protoplanetary Disk, planets around low-mass stars may typically be much smaller.  A second issue with fast forming planets is that they are much less likely to have enough time to collect enough water to support life.[002]


Nothing is absolute.  Gliese 581 is a Red Dwarf that has a number of large planets, and also has a debris disk that appears to have tens times amount of comet debris than our own Solar System.  This suggests low-mass stars can have habitable planets.  That said, Gliese 581 may be an outlier.  Other factors are obviously involved that need further study.

Primary reference:
S. N. Raymond, J. Scalo and V. S. Meadows, The Astrophysical Journal 669 (Nov., 2007) 606–614, arXiv:0707.1711 [astro-ph], A Decreased Probability of Habitable Planet Formation around Low-Mass Stars

Hacker News

Saturday, June 27, 2015

Lack of reproducibility of scientific papers getting attention

A lack of reproducibility of published scientific studies is finally getting recognition by the corporations (that seems to me to that could lose millions from bad research).  Academia seems a bit resist.  Source article:
 Reseach uncovering unreproducibility faces backlash 

Thursday, April 23, 2015

U.S. Space & Rocket Center of Huntsville, AL

On a recent trip to Huntsville, AL, I was able to squeeze enough time for myself to visit the world famous U.S. Space & Rocket Center.  When you first walk into the museum, the first couple of exhibits are a little underwhelming, given the grandeur of the purpose of the site.  There is a display of patented inventions, then a tribute to Dr. Wernher von Braun.

It is interesting, but very museum-like.  Where's the rockets?

Well, once you are thru there, you can go outside!  Rockets!  Rockets!  Rockets!  None of them blasting off, but still impressive, nonetheless.

Of course, there is a lot more than just rockets that go into space.  Without giving too much away, here's a few more photos.  This is really a place you should visit just to see the shear scale of these massive machines.

Saturday, December 06, 2014

"To good to be true" - Criticism of scientific studies grows

It is almost ironic, the other day I posted this article Reason Why I'm Skeptical of Skepticism which criticized over reliance on many study conclusions without actual supporting or valid data within the studies.  Now, just a few days later, there is a new published "study of studies" which reinforces the idea of being skeptical of scientific study conclusions, Excess Success for Psychology Articles in the Journal Science.  This study exposes that many studies in Psychology have issues, where the declared conclusions are simply "to good to be true" based on the strength of the data.  The inference being that there may be a general problem with all fields of science.
"Not every experiment is methodologically sound, and some experiments (even if methodologically sound) do not clarify the status of a theoretical idea. There is little reason to publish such experimental results, whether they are statistically significant or not. Unfortunately, in day-to-day scientific practice it is quite easy to interpret an unsuccessful outcome as being irrelevant to the theory or as being methodologically flawed and therefore not worth reporting."
In other words, data is cherry-picked in support of the theory rather than attempting to take contrary results into account.  This is basically throwing out the Scientific Method when it doesn't result in data this supports a theory.  In other cases, data collection is just too imprecise to form a suitable theory.  Kind of like garage-in-garbage-out.

I have a feeling a growing criticism of the current system is going to force changes into the process of study publishing and utilization.

Saturday, November 29, 2014

Reason why I'm skeptical of Skepticism

There is a plague on modern science and Skepticism.  That plague is over reliance upon research reports.  Research report is a gathering of pre-existing data (the "re" in "research"), repurposed to find patterns.  The problem is that many research reports are created to find correlations in support of predetermined conclusions (assumptions).  Research reports are often formatted as scientific studies and published in science journals along side scientific studies that use the Scientific Method.

What is the Scientific Method?  First, wonder about a phenomenon and ask a question.  Conduct research on that question.  Then, construct a hypothesis (a proposed explanation for the phenomenon). A hypothesis must be formed in such a way to be tested for being  false (falsifiability). The subsequent test must be done in such a way as to try to disprove your hypothesis.  Only after all of this can you analyze your data and form a conclusion from that data.  The final step is to share your results for others to review and check, often in the form of their own studies.  For a study to have value, its results must be replicated by others.1

The Scientific Method is valuable because it helps eliminate incorrect explanations for a phenomenon.  For example, say someone as a hypothesis that lemons are yellow because someone paints them with yellow paint.  You can test this in any number of ways.  You can go to an orchard and watch the lemons grow, changing color as they mature.  You can buy a lemon at a store and cut it, looking for a layer of paint.  You can peel the lemon and send the skin to a lab to search for significant amounts of paint.  Any of these tests would prove the hypothesis false.  Someone else could create a new hypothesis about why lemons are yellow, knowing that the cause is not paint.

The limitation of an unscientific research report is that it only requires you to visit a grocery store to see that the lemons are yellow in order to confirm your assumption that they've been painted yellow by a person.

Research reports often lack several crucial steps compared to Scientific Method.  First, the purpose of a research report is often to collect data in support of a pre-existing assumption.  An assumption is different than a hypothesis because an assumption is not a proposed explanation for a phenomenon; rather an assumption is that there is a phenomenon ("someone is painting those lemons yellow", instead of asking "why are lemons yellow?").  Second, no test is performed in support of this assumption.  Data is unscientifically collected from different studies, reports and other sources rather than being the results of a direct test.  There is certainly no falsifiability test.  Third, the results of the collected data are often correlated to the original assumption rather than standing on their own within the conclusion.

What's wrong with correlation between data sets?  Correlation is an indicator, but it is not a identifier. The common phrase is "correlation is not causation."  It is extremely easy to correlate unrelated things.  There is a website dedicated to just this.  This is why the Scientific Method requires a falsifiability test.  It eliminates the reliance on correlation.

Now, this is not to say all research reports are bad.  A research report that uses the Scientific Method to analyze data in a way that can be demonstrated with falsifiability does have value.  But, it is very hard tell good reports apart from bad reports using quick Twitter or reddit title links.  You have to read the report to know if it has value or if it is pseudoscience.  You have to read the whole report because the report's title and conclusions often do not even match-up the data within the report.

This is where I run into issues with Skepticism.  Skepticism tends consider any conclusions of a published research report (in support of presumed consensus) to be the same as studies using the Scientific Method.  Opinions regarding concepts outside the presumed consensus are immediately rejected (even if they are published) without regard to the quality of the report or study.  I cannot count how many times I've read a promoted research report, only to find that the evidence in the report is based correlated cherry-picked data.  Blind acceptance of research report conclusions is a big problem with Skepticism, especially as it grows in popularity among Atheists and other non-religious folks.  I've seen seen sources such as "skeptic" magazines that site unscientific research reports as though they are undeniable fact.  It is a problem being exacerbated by the ease with which (mis)information flows on the Internet through various social media and various other media outlets.

Other reading

In researching this topic, I found a very interesting "study of studies" about the flaws in most studies, Why most published research findings are false. Nothing in my article here is based on this study, so take this as a completely different source.  It is worth the read, and more fuel for the fire to be skeptical, not just of Skepticism, but of anyone trying to use a "study" to promote a notion.

Sunday, March 23, 2014

Sensless Sunday: Mammoth Star

  1. The last pyramids in Egypt where finished before the last of the Woolly Mammoths died out.1 2
  2. The World as we know it was designated to end by a Viking myth on 2/22/20143 and by a modern economist on 3/4/2014.4 The quote from War Games rings through my head right now about "We're still here! We're STILL HERE!".
  3. Our Solar System is traveling at an average speed of 514,000 mph relative to the Milky Way galactic center.5

Saturday, April 06, 2013

Remote Stone

Of what world we wonder true?  Our lacking nature holds fast our corporeal soul upon the bosom of thriving abodes that guise the cradled womb.  In this place stand we, me and all others, bound not in chains but yoked hereto nonetheless.  Grand thrusting spears slice through the wondrous  blue veil, floating on the currents of bent universe beyond this round realm, bringing to the helm  fleshless anthropomorphized cold creatures to cast away the dark cloak, thus revealing remote stone for stone’s sake.

Sunday, February 17, 2013

Senseless Sunday: Antarctica Water Pie

  1. Antarctica has two species of flowing planets: Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis).
  2. Boston Cream Pie is the the official state dessert of Massachusetts.  (Go figure.)
  3. Old trees can actually produce more carbon and methane than they absorb.[1]
  4. Currently, 400 species of sharks roam on the oceans of Earth.
  5. The fastest recorded swimming animal is the sailfish, which can swim  up to 68 mph.