Top Ten Posts of 2017

Now that we are at the end of 2017, I figured it was time to look back once again at this year’s material on Drew Ex Machina and see which of the 38 new essays I posted during this site’s fourth year online, along with earlier published material, proved to be most popular to my readers. In addition to satisfying my curiosity, this exercise is an attempt to figure out what kinds of articles my readers prefer so that I can focus my attention on similar topics over the coming months when possible. What follows is a review of the Top Ten most popular articles on this site during 2017 based on a raw tally of their page views. If you are interested in checking out any of these articles for yourself, they can be accessed by clicking on the titles or the feature images in the reviews that follow.

An artist’s impression showing how the binary star system of Sirius A and its diminutive blue companion, Sirius B, might appear to an interstellar visitor. (NASA, ESA and G. Bacon – STScI)

#10 New Hubble Observations of the Sirius System

With a V magnitude of -1.46, Sirius is the brightest star in the nighttime sky today. And at a distance of only 8.5 light years, it is also among the closest stars to our solar system. But like so many stars in our neighborhood, Sirius is actually a multiple star system. In addition to the bright A1V type star we readily see, the system also contains a dim V magnitude 8.6 white dwarf called Sirius B locked in an eccentric 50-year orbit. Since 1894, the presence of a third object has been suspected based telescopic observations as well as residual wobbles in the motions of Sirius A and B (see “Sirius: The Search for New Companions Continues“).

The #10 ranked article on Drew Ex Machina in 2017 took a fresh look at the properties of the stars in the Sirius system as well as the question of the presence of a third object. By combining 19 years of observations from NASA’s Hubble Space Telescope with 14 years of precision astrometric measurements from the US Naval Observatory as well as other ground-based observations stretching back to 1862, an updated orbit for Sirius A and B was determined allowing their properties to be characterize. In addition, they were able to place strict limits on the presence of a third body in this system. The possibility of a third stellar body has been categorically excluded leaving only the possibility that objects smaller than low-mass brown dwarfs may exist.

An artist’s depiction of Tau Ceti e and f (PHL@ UPR Arecibo)

#9 Habitable Planet Reality Check: Tau Ceti

Being the nearest single Sun-like star to our solar system, Tau Ceti has been of interest not only to scientists but fans of science fiction for decades. The #9 ranked article on Drew Ex Machina in 2017 took a fresh look at this system and updated information on its possible planetary system. An international collaboration of scientists working on various exoplanet surveys introduced a new data analysis technique which takes better account of the various sources of noise in precision radial velocity measurements allowing the detection of variations amounting to only a few tens of centimeters per second. Pooling radial velocity measurements for Tau Ceti from two long-term surveys, this group found evidence for the presence of four super-Earth-size exoplanet candidates including two first hinted in an earlier analysis from 2013 which some claimed were potentially habitable. While the prospects these two exoplanets are potentially habitable are not very good (assuming that their existence is confirmed), these new results begin to hint at the potential discoveries and problems which await astronomers as they introduce a new generation of instruments capable of even higher precision measurements.

Artist depiction of a habitable planet orbiting a red dwarf. (NASA/CfA/D. Aguilar)

#8 Habitable Planet Reality Check: The Nearby GJ 273 or Luyten’s Star

The year 2017 has proved to be a fruitful one for those interested in finding potentially habitable exoplanets. While NASA’s Kepler mission has grabbed the most headlines during the past few years, many ongoing ground-based surveys employing a range of techniques have also provided important results for stars much closer to us. Ranked at #8, this article reviewed the potential habitability of one of two exoplanets found orbiting the nearby red dwarf known as Luyten’s Star or GJ 273 located 12.4 light years away. Given what we know so far, it would appear that GJ 273b is a good candidate for being potentially habitable and is currently the second closest known example after Proxima Centauri b. Although much more needs to be learned about the exoplanets orbiting Luyten’s Star, they promise to be excellent targets for future investigations from the ground and space because of their proximity to the Sun and the host star’s relative brightness.

Artist depiction of an exoplanet. (NASA/Ames/JPL-Caltech)

#7 Habitable Planet Reality Check: Wolf 1061c Revisited

In December 2015 the discovery of three exoplanets orbiting Wolf 1061 was announced by a team of Australian astronomers using publicly available precision radial velocity measurements. One of those exoplanets, Wolf 1061c, was even thought to be potentially habitable (see “Habitable Planet Reality Check: Wolf 1061”). The #7 ranked article for 2017 took a fresh look at the question of this world’s potential habitability given updated properties based on a new analysis of an expanded radial velocity data set. While there are still many outstanding questions about the potential habitability of any exoplanet orbiting red dwarfs, the new assessment does seem to increase the odds that Wolf 1061c is potentially habitable and a worthy target for future study.

The crew of Apollo 1 poses at LC-34 on January 17, 1967 – ten days before the pad fire which killed them. (NASA)

#6 The Future That Never Came: The Unflown Mission of Apollo 1

On January 27, 1967, NASA astronauts Gus Grissom, Ed White and Roger Chaffee perished in an accidental spacecraft fire during what should have been a routine countdown rehearsal for the Apollo 1 mission. This tragic accident brought NASA’s Apollo mission to a virtual halt as the accident was investigated casting doubts on the prospects of landing men on the Moon before the end of the decade. The #6 ranked article for 2017 took a close look at the preparations for this flight as well as the details of the plans for a two-week mission that was to have launched on February 21 had the pad fire not occurred.

A view of Apollo 4 at LC-39A prior to its launch. (NASA)

#5 Apollo 4: The First Flight of the Saturn V

On November 9, 1967 Apollo 4 lifted off from Pad A of Launch Complex 39 for the first unmanned test flight of the Saturn V – the world’s largest rocket which would be used to send Apollo missions to the Moon. The #5 most popular article on Drew Ex Machina for 2017 took a close look at this historic mission. Unlike earlier test flights of large rockets, the decision had been made four years earlier that this first Saturn V test flight would be an all up test with three live stages in an effort to speed the program’s schedule and help constrain costs. Fortunately, the gamble paid off with a fully successful mission ending 8 hours and 37 minutes after launch with the splashdown of the Apollo 4 Command Module in the Pacific Ocean.

Artist’s conception of the probable planet orbiting the star called Lalande 21185 or GJ 411. (Ricardo Ramirez)

#4 Our New Neighbor Orbiting Lalande 21185

While NASA’s Kepler mission has tended to find exoplanets hundreds of light years away or more, there have been a number of systematic surveys made of stars much closer to home over the last half century. Among these is the nearby red dwarf Lalande 21185 – the fourth closest main sequence star system known today after α Centauri, Barnard’s Star and Wolf 359 (see this site’s Alpha Centauri page, Barnard’s Star page and “The Real Wolf 359” for more on these stars). The #4 ranked article in Drew Ex Machina in 2017 reviewed the rather checkered history of exoplanet discovery claims for this neighbor stretching back to 1960. The announcement in February of the discovery of a hot, super-Earth-size exoplanet (and the lack of any evidence to support earlier claims) seems to have finally settled the question of whether or not Lalande 21185 supports a planetary system.

Artist rendering of a planet of the sort that NASA’s Kepler mission has observed. (NASA/JPL-Caltech)

#3 Habitable Planet Reality Check: Kepler’s New Planet Candidates

The primary objective of NASA’s Kepler mission was to determine how common rocky planets are in the habitable zone (HZ) with the ability to detect Earth-size planets in Earth-like orbits around Sun-like stars (i.e. true “Earth twins”) being the primary driver for the design of the spacecraft and its observation strategy. Assuming that our Earth is typical of life-bearing planets in the universe, this is the best place to start looking for habitable worlds outside of our solar system (see this site’s Kepler page for articles on this mission). As work on Kepler’s primary mission has been officially winding down, project scientists have been publishing the final results from their analysis of Kepler’s huge data base. The #3 article on Drew Ex Machina for 2017 took a closer look at the potential habitability of Kepler’s most promising exoplanet candidates – objects of interest which still require follow up observations in order to verify their planetary nature. Among these candidates are objects which seem to be the closest thing the Kepler mission has found to being a true Earth-twin.

Artist’s depiction of an Earth-like Kepler 186f. (NASA Ames/SETI Institute/JPL-CalTech)

#2 Habitable Planet Reality Check: Kepler 186f Revisited

In response to this unhealthy trend in the scientific community and especially the media overstating the potential habitability of newly discovered exoplanets, I started the “Habitable Planet Reality Check” series of articles on Drew Ex Machina shortly after the web site was established (see this site’s Planetary Habitability page for a complete listing of these and related articles). In these articles I have attempted to cut through the hype to give an honest assessment on the potential habitability of various exoplanets based on the best available analysis of the observations and the current scientific understanding of planetary habitability. For the first in this series of articles, I examined the case of Kepler 186f whose discovery was announced April 17, 2014 – just three weeks after Drew Ex Machina came online (see “Habitable Planet Reality Check: Kepler 186f“).

While I originally started out in my first review in 2014 with the intent of debunking the claim, it turns out that Kepler 186f appears to have among the best chances of being potentially habitable of all exoplanets currently known. In the second-most popular essay on Drew Ex Machina in 2017 (which was ranked at #2 in 2016 as well), I revisited the case for Kepler 186f and reassess its potential habitability given what we have learned about it and other exoplanets over the intervening two years. The new data presented in the updated assessment published on the second anniversary of this world’s discovery only strengthens the case for this distant exoplanet’s promising prospects.

This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. (ESO/N. Bartmann/spaceengine.org)

#1 Habitable Planet Reality Check: The Seven Planets of TRAPPIST-1

Among the most exciting astronomical discoveries of 2017 was the detection of seven exoplanets orbiting the nearby ultracool dwarf star known as TRAPPIST-1, named after the European Southern Observatory’s (ESO’s) TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope which spotted the transits of these exoplanets. Most exciting of all was that as many as three of these exoplanets have some genuine prospects of being potentially habitable. The #1 ranked article in Drew Ex Machina for 2017 took a close look into the details of the discovery of this system of planets as well as an initial assessment of the habitability prospects for TRAPPIST-1e, f and g. This system, along with other nearby transiting exoplanetary systems, should provide scientists with their best near-term prospects for probing the limits of Earth-like habitability using a new generation of astronomical instruments which are beginning to come online.

I would like to take this opportunity to thank the almost 102,000 people from around the globe who have taken time to read these Top Ten as well as many of the other 218 essays on Drew Ex Machina during 2017. The many comments and feedback on this site as well as in other forums have also been greatly appreciated. I intend to continue posting interesting essays on space-related topics during 2018 and hope that all of you continue reading and enjoying them.

Happy New Year!   Drew LePage

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