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Paul Carr
Attended Johns Hopkins University
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Paul Carr

Space Missions  - 
Dwarf planet Ceres might have right stuff for life:
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Paul Carr

Discussion  - 
Maybe this is a FAQ, but it true that it is no longer necessary for someone to log into G+ to join a hangout?
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I think hangouts upgrades are still optional, but I'm still doing it from g+ because of reports that our school's firewall is blocking the service after upgrading.
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Paul Carr

Good Science Podcasts  - 
Chippie Siththanandan, David W. Zhang, Diego Calderon, Emily C. Glassberg, Episode, Koshlan Mayer-Blackwell, Lisl Esherick, Maulik Kamdar, Scot Kravitz, Trisha Stan, Tyler Stukenbroeker, Vanessa Sochat · Episode 73: Fight Back with Science. Author StanfordTree Date March 26, 2015 ...
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Paul Carr

All about Software  - 
This is probably a FAQ, but can someone point me to resources for disguising an anonymous person's voice? I use both Reaper and Audacity.
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Try the ReaPitch plugin in Reaper. Just play with the sliders a bit. You should be able to change your anonymous person's voice enough to make it unrecognizable.
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Paul Carr

I need help  - 
Looking for one more team member, someone who can produce, host, write, promote, the whole shebang. Season 3 starts around August of this year, which is about the timeframe we are looking at.
I'd like to put this podcast out on a more frequent basis, but I can't do that on my own. It requires too much time I don't have. I enjoy the process, so it doesn't feel like work, but it does take lots of time. I also want m...
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Just got another scam phone call from the "maintenance department of the operating system that is running on the Windows." A guy with a heavy accent called himself Allan Ray. Who could possible be falling for this crap?
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Paul Carr

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The most viewed #wowsignal log entry for quite some time:
Release Date: 20 December 2014 download the .mp3 audio file Nora Noffke, Associate Professor in the Department of Ocean, Earth and Atmospheric Sciences at Old Dominion University, tells us about her recent hypothesis paper ...
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Have him in circles
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Paul Carr

Astronomy  - 
Astronomers have spotted a never-before-seen phenomenon in our solar system's asteroid belt: a space rock with six tails, spewing dust from its nucleus like spouts of water radiating from a lawn sprinkler.
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The photos are much more realistic than 6 perfectly symmetric tails depicted by the artistic image intended to grab attention.
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Paul Carr

General  - 
(Journal Juice) Did the Earth have to form twice?

This story start with me being (somewhat unfairly) annoyed at +IFLScience and finishes with me being (slightly more justifiably) annoyed at the original research paper. The former of the two offensive pieces is here:

And my wrath is a little overdone since, in truth, there's really only one line that irritates me. Its crime is that (a) it's wrong and (b) its wrongness unsells the research's message. That offending line is this one:

"Jupiter migrated inwards, they found, from an orbit of more than 5 astronomical units (AUs) to around 1.5 AUs (where Mars' orbit is today)."

Except they didn't find, because the above description of Jupiter's wild adolescence is fast becoming a standard in Solar System formation theory. And that is part of the excitement.

Named after the sailing term where a boat swings around in a U-turn, the 'Grand Tack' scenario depicts Jupiter moving from somewhere close to its current location between 3 - 10 AU (1 AU = Earth-sun distance) to around 1.5 AU, whereupon it is pulled back due to the influence of Saturn. 

This was first suggested in 1999 by Frederic Masset and Mark Snellgrove while at Queen Mary College in London. The name was then later coined when Kevin Walsh, Alessandro Morbidelli, Sean Raymond, David O'Brian and Avi Mandell picked up the idea in a letter to Nature in 2011, pointing out that this model can naturally explain the diminutive size of Mars. 

While such motion from a giant planet sounds contrived, the Grand Tack actually has a lot of merit for the following reasons:

1. Firstly, we know Jupiter had to migrate. If a planet grows to around 10 x Earth's mass while the star is still surrounded by its natal disc of gas, the influence of the gas on the planet will drag it inwards in a process known as 'Type II migration'. Since our gas giants are substantially larger than 10 Earth masses and must have acquired their gigantic atmospheres from the gas disc, this must have occurred while they were forming.

This leaves the question: how are they in their current positions?

Observations of solar systems outside our own show a large population of 'hot Jupiters', where gas giants have been dragged inwards to a cosy rendezvous with their star. Yet, somehow our planets avoided this miserable fate.

2. Secondly, Mars is squiffy. As you step away from the sun, its gravitational pull lessens. This should allow planet mass to increase and indeed, the Earth is larger than Venus which is larger than Mercury. Then there's Mars which —according to such an idea— should be larger than the Earth, but is in fact only 1/10th of its mass. 

3. Just beyond Mars is a collection of rocks orbiting the sun known as the Asteroid belt. These come in two different flavours 'S-type' and 'C-type', the latter of which contain water similar to Earth. Yet, if these guys all formed around the same point in the Solar System, why are there different types?

The Grand Tack explains all these problems very neatly. Jupiter does indeed migrate, moving towards the inner Solar System. Its movement shepherds small rocky planetesimals ahead of it like a giant snowplough. This mixes up the original S-type rocks in the terrestrial region with the icy C-type rocks that originally formed further out but have been shuffled inwards by Jupiter. 

As Jupiter approaches the outer edge of the terrestrial planet forming region, Saturn catches up. Growing slower than Jupiter, it begins its own migration later and doesn't chase down its bigger brother until Jupiter reaches a distance of around 1.5 AU. Saturn's presence blocks out part of the gas disc's interaction and the resulting force pulls Jupiter back, turning it around in the U-turn that earns the scenario its name. 

The result of Jupiter getting up close and personal is a clearing out of material up to around 1 AU, leaving Mars with very few planetesimals to build up its mass. This gives a small Mars, a mixed asteroid belt and doesn't require any magic to stop Jupiter feeling the migrating pull of the gas disc. Hoorah! 

This is why this theory is popular. 

In a new paper by Konstantin Batygin and Greg Laughlin, it is proposed that this same mechanism can also explain why our Solar System lacks hot super-Earths. 

In this research, Batygin and Laughlin suggest that the shepherding of rocky planetesimal by Jupiter's inward migration could set off a collision apocalypse through the inner Solar System. This ultimately leads to a clear out of planets already chillin' in this region, including any super-Earths. Our own terrestrial planets then had to form after Jupiter's departure, as a second evolution after a dramatic planet extinction. 

The idea is that as Jupiter begins to plough up the planetesimals in front of its motion, it increases their collisions. These collisions grind down the planetesimals from 10 - 100 km sized rocks to ones dropping below the 1 km size range. At this point, these smaller boulders begin to feel the drag of the gas disc. 

Because solid particles do not feel pressure, planetesimals orbit the sun slightly faster than the gas. This produces a head wind that bigger rocks can ignore, but drags on smaller rocks to slow their motion. As the planetesimals are ground down in size, this head wind becomes a major issue and they break away from Jupiter to start a rapid progression towards the sun. 

Any planets between Jupiter and the sun will therefore be subjected to a wave of these small rocks. If there is enough of them, this can overwhelm the planet orbit's stability and crash it into the sun. 

This idea has a number of positive points and —in my opinion— a few over-reached one. 

On the definite plus side, this collisional cascade seems convincing. It's a straight forward consequence of a theory that's already proved its salt and could well have serious implications for planet formation. 

It also solves a mystery the authors highlighted with regard to formation times. While the planetesimal planet building blocks are thought to have formed within 1 million years of the sun's birth, chemical analysis suggests the terrestrial planets didn't form for another few hundred million years. This delay is explained if our rocky worlds are the second generation of planets to form, after Jupiter has taken out the first attempt.

An additional bonus is an explanation for why we do not see any planets inside Mercury's orbit. Planets on very short orbits most likely arrive there by sauntering in via migration from a cooler spot further out. This requires the gas disc to pull the planet inwards. If our terrestrial planets were the second generation to form, then the gas disc might not have been around long enough to drag anyone into a snugger orbit.  

However, the authors make some pretty mighty claims as to the consequences of this effect which I feel are a lot less certain.  

1. To begin with, the authors focus on the destruction of super-Earths in our solar system. Yet, there is really no evidence that we ever had these planets.

The formation mechanism of planets with masses between the Earth and Neptune remains a subject of intense debate. Did they form similarly to the Earth, but with an over zealous efficiency that allowed super-sized variations? Or are they gas giants like Neptune which migrated inwards towards sun? Without understanding their formation, it is impossible to assess whether our Solar System likely hosted this kind of world. 

The authors specifically do not attempt to address the formation of super-Earths. Rather, they argue that as the most common type of exoplanet discovered, it is statistically likely that we too once had this population. 

The problem with this argument is one of completeness. Observations of exoplanets are most sensitive to large planets that orbit close to their star, meaning that we detect hot super-Earths more easily than planets that are further out. This makes it inevitable that we will dramatically overestimate the fraction of stars that have this particular planetary configuration. 

The authors also argue that the total mass of our terrestrial planets is low compared to observed exoplanet systems, supporting a mass clean-out sometime in the past. This  suffers from the same problem as the above: if we don't know how the super-Earths came to reside close to their star, it's not possible to compare mass distributions. For example, if they had migrated their chunky selves from far out in the disc, then comparing the mass in just our terrestrial region is hardly playing fair. Moreover, we know Jupiter ejected truck loads of rocks due to the presence of the Oort cloud; a massive collection of boulders that encircles our Solar System right at the brink of the sun's gravitational hold. This also needs to be accounted for when comparing quantities of material. 

This doesn't completely invalidate the paper's argument. It still stands that if we had super-Earths and if they formed and migrated towards the sun before Jupiter began to move, then they could have been destroyed. It's just a lot more ifs than the paper implied, which used the term 'ubiquitous' far more than was decent. 

2. Just to really press every button on the media fanfare, the paper ends with the highly provocative statement:

"Most dramatically, our work implies that the majority of Earth-mass planets are strongly enriched in volatile elements and are uninhabitable."

It's not immediately clear from the paper where this statement comes from, but a little help from the press release points to the answer: the first generation of planets would have formed much earlier than our current terrestrial population. This would have meant they acquired thick hydrogen atmospheres from the protoplanetary disc, making their air an unbreathable fug. If a solar system doesn't have a Jupiter to wreck this planet population, then nothing with an Earth-like atmosphere stands a chance of forming.

This is again a possible scenario, but it also has such a huge number of 'ifs', 'buts' and 'maybes' that it's really not a conclusion to this paper. 

For a start, an Earth-sized planet is not massive enough to hold onto a hydrogen atmosphere. Our first atmosphere would have comprised of mainly hydrogen and helium, but these were replaced by gases from the planet's interior. It's not clear to me why this wouldn't happen in the same fashion, even if our planet formed earlier with an initially thicker hydrogen atmosphere.

It is possible the authors meant to propose that the first generation of planets were super-Earths in size, and therefore capable of holding onto their hydrogen atmosphere. This runs us smack-bang into the aforementioned issue of not knowing how super-Earths form. Without knowing this, we cannot predict their atmospheres. 

… also, if the first generation of planets typically hangs out by the sun, then breathable air is the least of the issue. 

Generally, I thought the paper pointed out a probable and interesting phase in our Solar System's formation. However, the suggested consequences were too far reached with not enough discussion as to their true probability. In short: sensationalism was picked over realism. 

(Photo credit: Kouji Kanba.
Journal paper:
Press release:

#exoplanets #astronomy #habitablezone
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Paul Carr

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Venus exploration with two experts on the subject: David Grinspoon and Geoffrey Landis.
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Under-explored Venus....really enjoyed listening, thanks Paul!
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Space Systems Engineer, blogger, podcaster, investigator
I suffer from a low curiosity threshold.  I am a space systems engineer, blogger, podcaster and a skeptical but open-minded investigator.   Especially interested in space, astronomy, and the search for intelligent ETs.  Although most of my G+ posts are science or space related, I also spout off on music from time, totally unqualified though I am.

Trying to keep my middle-aged body in shape and a bit safer by learning Krav Maga.  Train at Pure Performance Martial Arts in Rockville, Maryland.

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I am not a member of any political tribe.
Bragging rights
I killed a satellite in space. On purpose. Also, earned a black belt in Tae Kwon Do at age 45.
Space Mission Systems Engineer
Exactly failing to please the eye. Getting the hang of Thursdays (often enough). Looming. Shouting (I'm really very good at shouting). Space mission design, analysis and execution.
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