Across the Universe: Fast changes
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Sunrise in June from the Papal Palace in Castel Gandolfo. This particular sunrise occurred during the Transit of Venus on June 6, 2012

This column first ran in The Tablet in June 2013

Summer began [in 2013] on Friday morning, 21 June, at 5:14 am GMT...in the northern hemisphere, of course; south of the equator, it’s winter. [The summer solstice 2017 in Northern Hemisphere occurred at 4:24 am GMT on Wednesday, June 21.]

This definition is based on the precise orientation of the Earth in its orbit. The Earth is tilted relative to its orbit, and like a gyroscope its spin axis stays pointed in the same direction, year round. In a convenient coincidence for navigators, our north pole is pointed near the star Polaris. Polaris is not directly above the Sun; it’s directly above Earth’s tilted spin axis. In June, the Earth is in the part of its orbit where it’s on one side of the Sun, and Polaris is on the other side. The northern half of the Earth, tilted towards Polaris, is also tilted towards the Sun; that’s why it gets warmer. The moment when Sun and Polaris are exactly lined up is the solstice, the beginning of our northern summer; that’s what occurred on June 21. Since the other hemisphere is pointed away, it’s winter there. Six months later, December 21, the positions and the seasons are reversed.

Julius Caesar’s “365 days plus a leap year” calendar almost exactly matched the time interval from solstice to solstice – off by less than a day per century. But after 1500 years the error had built up to ten days. Thus Pope Gregory XIII hired some astronomers to tweak the calendar, the first incarnation of the Vatican Observatory.

In the north we see the Sun in the southern sky; Australia always sees it in the north. In effect, we’re looking past the equator towards the Sun. When I lived in Kenya, on the equator, as the year progressed the Sun would first warm the northern half of my apartment, then move to warm the southern side. But what I also noticed in Kenya was that, even with the Sun spending as much time on one side as the other, January was actually much warmer than July. That’s because the Earth’s orbit is an ellipse, not a perfect circle. We are actually closer to the Sun in early January, and furthest away on the 4th of July. (Notice there’s about a five fewer days of northern winter than northern summer – recall how February’s shortchanged. Because of our elliptical orbit we move faster through the northern winter months.)

But the ellipticity of Earth’s orbit, and the position and tilt of our axis, are all items that slowly change with time. Over tens to hundreds of thousands of years, as they change our climate changes. We can see this in the geological record.

A slightly warmer winter in the north means we have moister, hence snowier, winters than in the south. As it happens there’s more landmass in the north, as well, to accumulate this snow. This accident of northern continental positions with warm wet winters, thanks to Earth’s current orbit, means we are actually in a mini ice age right now. Until recently, this has been carefully balanced by the carbon dioxide in the atmosphere, which keeps us from freezing over.

The issue with climate change isn’t that it’s changing; it has always changed. The problem is the rate of change. In the past fifty years the carbon dioxide has increased by 25%, hitting 400 ppm [in 2013]. That's faster than our human institutions can cope. Our cities are not built to withstand the energetic storms that become more common when more carbon dioxide holds more energy in the air. Our seaports are vulnerable to a rising sea level as the pole caps melt.

In our own lives we make free choices, within parameters set by circumstances beyond our control. Likewise, dealing with climate change the trick is to find those things we actually can do something about; and then make wise choices.

Also in Across the Universe

  1. Across the Universe: What’s in a Name?
  2. Across the Universe: Fools from the East
  3. Across the Universe: Hunches
  4. Across the Universe: Desert or a dessert?
  5. Across the Universe: Stardust messages
  6. Across the Universe: The best way to travel
  7. Across the Universe: Original Proof
  8. Across the Universe: Pearls among Swine
  9. Across the Universe: One Fix Leads to Another
  10. Across the Universe: Limits to Understanding
  11. Across the Universe: The Glory of a Giant
  12. Across the Universe: Fire and Ice
  13. Across the Universe: Science as Story
  14. Across the Universe: Recognition
  15. Across the Universe: Tending Towards Paganism
  16. Across the Universe: The Ethics of Extraterrestrials
  17. Across the Universe: Orbiting a New Sun
  18. Across the Universe: Seeing the Light
  19. Across the Universe: DIY Religion
  20. Across the Universe: Truth, Beauty, and a Good Lawyer
  21. Across the Universe: Techie Dreams
  22. Across the Universe: By Paper, to the Stars
  23. Across the Universe: Transit of Venus
  24. Across the Universe: Ordinary Time
  25. Across the Universe: Deep Impact
  26. Across the Universe: New Worlds
  27. Across the Universe: Tom Swift and his Helium Pycnometer
  28. Across the Universe: Tradition… and Pluto
  29. Across the Universe: Bucks or Buck Rogers?
  30. Across the Universe: Key to the Sea and Sky
  31. Across the Universe: Off The Beach
  32. Across the Universe: All of the Above
  33. From the Tablet: Tales of Earthlings
  34. Across the Universe: Heavenly peace?
  35. Across the Universe: Help My Unbelief
  36. Across the Universe: Stories of Another World
  37. Across the Universe: Planetary Counsels
  38. Across the Universe: Words that Change Reality
  39. Across the Universe: New Heavens, New Earth
  40. Across the Universe: Souvenirs from Space
  41. Across the Universe: For the love of the stars…
  42. Across the Universe: Spicy planet stories
  43. Across the Universe: Asking the right questions
  44. Across the Universe: Everything You Know Is Wrong
  45. Across the Universe: Errata
  46. Across the Universe: Clouds of Unknowing
  47. Across the Universe: Being Asked the Right Questions
  48. Across the Universe: Recognizing the Star
  49. Across the Universe: Heavenly Visitors
  50. Across the Universe: Christmas Presence
  51. Across the Universe: When Reason Itself Becomes Flesh
  52. Across the Universe: Spinning our Hopes
  53. Across the Universe: Relish the Red Planet
  54. Across the Universe: Obedience
  55. Across the Universe: Traveling Light
  56. Across the Universe: The Still Voice in the Chaos
  57. Across the Universe: Europa
  58. Across the Universe: Defamiliarization
  59. Across the Universe: Forbidden Transitions
  60. Across the Universe: Genre and Truth
  61. Across the Universe: False Economies
  62. Across the Universe: Reflections on a Mirror
  63. Across the Universe: Japan
  64. From the Tablet: Why is Easter So Early This Year?
  65. Across the Universe: Oops!
  66. Across the Universe: Dramatic Science
  67. Across the Universe: Me and My Shadows
  68. Across the Universe: Touch the Sky
  69. Across the Universe: The Eye of the Lynx
  70. Across the Universe: Treasure from Heaven
  71. Across the Universe: Gift of Tongues
  72. Across the Universe: Maverick Genius
  73. Across the Universe: Awareness
  74. Across the Universe: Friends in high places
  75. Across the Universe: A Moving Experience
  76. Across the Universe: Grain of truth
  77. Across the Universe: Clerical Work
  78. Across the Universe: Teaching new stars
  79. Across the Universe: Science for the Masses
  80. Across the Universe: Changelings
  81. Across the Universe: Three Lunatic Answers
  82. Across the Universe: Dawn of My Belief
  83. Across the Universe: Martian Sunrise
  84. Across the Universe: Under the Southern Cross
  85. Across the Universe: Clouds from Both Sides
  86. Across the Universe: The Year (2011) in Astronomy
  87. Across the Universe: Jabberwocky and the Curious Cat
  88. Across the Universe: Waiting for the Call
  89. From the Tablet: God is dead; long live the eternal God
  90. Across the Universe: Taking the Heat
  91. Across the Universe: Stellar Round Up
  92. Across the Universe: A Damp Kaboom
  93. Across the Universe: Featureless Features
  94. Across the Universe: Confronting Fear and Terror
  95. Across the Universe: Eye Candy
  96. Across the Universe: The New Paganism
  97. Across the Universe: Immigrant Stars
  98. Across the Universe: Heavenly Visitors
  99. Across the Universe: Christmas Presence
  100. Across the Universe: When reason itself becomes flesh
  101. Across the Universe: Recognizing the Star
  102. Across the Universe: Awaiting the stars
  103. Across the Universe: Tides in our affairs
  104. Across the Universe: A Piece of the Action
  105. Across the Universe: Forced Perspective
  106. Across the Universe: Touched by Heaven
  107. Across the Universe: View from afar
  108. Across the Universe: What good is God?
  109. Across the Universe: Global warning
  110. From The Tablet: Precisely Strange
  111. Across the Universe: Faith and Expectations
  112. Across the Universe: The Boundaries of the Unknown
  113. Across the Universe: Happy Birthday to Us
  114. Across the Universe: Words, Words, Worlds
  115. Across the Universe: Rocket Science
  116. Across the Universe: Maybe
  117. Across the Universe: Perturbing the Universe
  118. Across the Universe: Edge of the World
  119. Across the Universe: A Thousand Stars are Born
  120. Across the Universe: Expect Surprises
  121. Across the Universe: Song of Praise
  122. Across the Universe: Jesuit Science
  123. Across the Universe: Of stars and sheep
  124. Across the Universe: Ephemeral science
  125. Across the Universe: Fast changes

View the entire series

In the Sky this Week – June 22, 2017
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The planet Venus appears high in the eastern morning sky; the bright star Capella, to the northwest, is the last star to fade with the oncoming dawn.

5 AM June 22 2017 Eastern Sky

Venus high in the eastern pre-dawn sky at 5 AM on June 22, 2017. Venus' orbit is shown in red. Image credit: Stellarium / Bob Trembley

The waning crescent Moon will vanish amid the morning haze to the east, to reappear in the west as a waxing crescent after dusk on June 25th.

9 PM June 25 2017 Western Sky

Crescent Moon appears after dusk in the western sky on June 25, 2017. Image credit: Stellarium / Bob Trembley

The Summer Triangle is an asterism formed from the three stars Altair, Deneb, and Vega, the brightest stars in the three constellations of Aquila, Cygnus, and Lyra. They can be see in the eastern sky before midnight.

11 PM June 22 2017 Eastern Sky

The Summer Triangle rises in the eastern sky before midnight on June 22, 2017. Image credit: Stellarium / Bob Trembley

Jupiter is high in the southwestern sky after dusk, and sets in the west around 1:30 AM. Saturn appears high in the southeastern sky after dusk, is at its highest around midnight, and sets in the southwest just before dawn.

11 PM June 22 2017 South-Western Sky

Jupiter and Saturn high in the southern skies at 11 PM on June 22, 2017. Jupiter and Saturn's orbits are shown in red. Image credit: Stellarium / Bob Trembley

Directly overhead, the Milky Way flows through the constellations Cygnus and Aquila (if you live in a city - trust me, it's really there... drive out of the city at night and have a look!). The constellation Cygnus contains a smaller and easy-to-spot asterism known as the Northern Cross.

Overhead at 11 PM on June 22, 2017

Several constellations and deep-sky objects are directly overhead at 11 PM on June 22, 2017. Image credit: Stellarium / Bob Trembley

The bright star Vega, part of the Summer Triangle, draws the eye to a fainter set of four stars in the shape of a parallelogram forming the constellation Lyra, Opposite Vega, on the short length of the parallelogram, lies an astronomical treat for the telescopic observer - M57, The Ring Nebula.

M57 Position

Position of M57 - The Ring Nebula in Lyra. Image credit: Stellarium / Bob Trembley

In a small telescope, the Ring Nebula appears as a hazy greenish ring; using a much larger orbiting space telescope, it's rather more spectacular!

M57 The Ring Nebula

M57, The Ring Nebula in Lyra. Image Credit: NASA/Hubble Heritage

Constellation-hopping from Cygnus through Lyra, we come upon the constellation Hercules; the core stars of Hercules form a trapezoid. On the widest edge of that trapezoid, farthest from Vega, is M13, the Great Cluster in Hercules.

M13 Position

Position of M13 - The Great Cluster in Hercules. Image credit: Stellarium / Bob Trembley

M13 appears as a fuzz-ball in smaller telescopes, but in larger 'scopes, individual stars resolve, and many sparkle like diamonds - it's absolutely gorgeous!

Hubble image of M13

Hubble catches an instantaneous glimpse of many hundreds of thousands of stars moving about in the globular cluster M13, one of the brightest and best-known globular clusters in the northern sky. This glittering metropolis of stars is easily found in the winter sky in the constellation Hercules. This image is a composite of archival Hubble data taken with the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys. Observations from four separate science proposals taken in November 1999, April 2000, August 2005, and April 2006 were used. The image includes broadband filters that isolate light from the blue, visible, and infrared portions of the spectrum. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Zoomable image of M13

Astronomers find Conclusive Evidence for Intelligent Life on Another Planet!
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Have you ever wondered what would happen if major media outlets reported that astronomers had finally found hard scientific evidence that intelligent life exists on another planet? What would be the effect on society? On religion? How would people react? Would we be alarmed, and riot in the streets? Would we all come together and finally have world peace? Would it be the biggest event in human history? Well, wonder no more—it has happened! Surely you have seen the news reported in the New York Times, the Wall Street Journal, and other media outlets?

You haven’t? Well, it’s not because they didn’t report it! Indeed, the Wall Street Journal stated on the front page that—

The most extraordinary development [of the year] has been the proof afforded by the astronomical observations of the year that conscious, intelligent life exists upon the planet Mars.

This is from the Wall Street Journal “Review and Outlook—Mars”, December 28, 1907 (Morning Edition), front page. That’s probably why you haven’t seen the news! The Journal went on to say—

There could be no more wonderful achievement than this, to establish the fact of life upon another planet. For there can be no doubt that from this point our knowledge of Mars must increase steadily through the coming years, and it is by no means an impossible stretch of the imagination to believe that as our mastery over electrical forces [by this is meant wireless communication, or radio] becomes more complete, we may be able before the present century ends to establish some sort of communication with the people of Mars. That a more complete knowledge of the planet Mars may possibly have a profound effect upon life on our own globe goes without question.

The Journal was not alone. The previous year the New York Times had a headline of “There is Life on the Planet Mars”. What was all this about?

From the New York Times, December 9, 1906.

From the New York Times, December 9, 1906.

You see, toward the end of the nineteenth century, telescopes had become good enough for astronomers to be able to see fine detail on planets. Also, recall from a previous pair of posts on William Whewell that astronomers had long assumed that intelligent life was plentiful in the solar system—with one nineteenth-century writer estimating the number of intelligent inhabitants of the solar system at 22 trillion—while Whewell argued otherwise. Astronomers began to make fairly detailed maps of Mars during this time. These maps showed polar caps on Mars (like on Earth), showed light and dark areas that seemed to change in color over the Martian year. They also showed, as seen in the figure above, a lot of fine lines criss-crossing the planet.

The fine lines became a point of particular interest. Were these natural features?—simply channels or fractures of some sort in the planet's surface? Or were they artificially constructed? Were they, in fact, canals on Mars? If they were canals, then they would imply a very technologically advanced Martian civilization. A network of canals spanning the globe was far beyond the technology of Earth in the late 19th century (and far beyond the technology of Earth today in the early 21st century). The theory that the lines on Mars were canals was promoted by a number of people; including the French astronomy popularizer Camille Flammarion, who in his 1892 book La planète Mars et ses conditions d’habitabilité argued that Mars was inhabited by a race of beings superior to humans; and also including Giovanni Schiaparelli, who in an 1898 paper speculated about how the changing appearance of the Martian canals could be explained by the actions of a Martian “Minister of Agriculture” and Martian engineers, who filled canals for irrigation when the spring growing season arrived on Mars, and who all worked under a global Martian socialist government.

Left - Vatican Observatory Director Br. Guy Consolmagno, S. J., pointing out to visitors an old Mars globe in the V.O.'s collection.  Right - note the 'canals'.

Left - Vatican Observatory Director Br. Guy Consolmagno, S. J., pointing out to visitors an old Mars globe in the V.O.'s collection. Right - note the 'canals'.

The American astronomer Percival Lowell built an observatory in Arizona (it’s still there) for the purpose of studying Mars. Lowell and his staff detected still more canals—bigger ones, smaller ones—with dark areas (“oases”) near the intersections of canals. Lowell wrote in his 1906 book Mars and Its Canals

We are led to the conclusion that the canals are strips of vegetation fed by water from the polar caps, and that the floral seasons there as affecting the canals are conditioned, not as they would be with us, directly upon the return of the sun, but indirectly so through its direct effect upon the polar snows.

—furthermore, he said, the arrangement of the canals argued that they were artificial in origin—

For we find ourselves confronted in the canals and oases by precisely the appearances a priori reasoning proves should show were the planet inhabited. Our abstract prognostications have taken concrete form. Here in these rectilineal lines and roundish spots we have spread out our centres of effort and our lines of communication. For the oases are clearly ganglia to which the canals play the part of nerves. The strange geometricism which proves inexplicable on any other hypothesis now shows itself of the essence of the solution. The appearance of artificiality cast up at the phenomena in disproof vindicates itself as the vital point in the whole matter. Like the cachet of an architect, it is the thing about the building that established the authorship.

Lowell argued that any apparent “seas” on Mars were simply areas of vegetation, and that Mars was a dry planet. Like Schiaparelli, he argued that the purpose of the canals was to provide a global water supply—

So far as we can see the only available water is what comes from the semi-annual melting at one or the other cap of the snow accumulated there during the previous winter. Beyond this there is none except for what may be present in the air. Now, water is absolutely essential to all forms of life; no organisms can exist without it.

But as a planet ages, it loses its oceans... and gradually its whole water supply. Life upon its surface is confronted by a growing scarcity of this essential to existence. For its fauna to survive it must utilize all it can get. To this end it would be obliged to put forth its chief endeavors, and the outcome of such work would result in a deformation of the disk indicative of its presence. Lines of communication for water purposes, between the polar caps, on the one hand, and the centres of population, on the other, would be the artificial markings we should expect to perceive.

Lowell’s staff even obtained photographs of thirty-eight canals, despite the fact that photography at the time was poorly suited to capturing fleeting detail. Lowell thought that his theory of intelligent life on Mars was the best explanation, and really the only explanation, of Mars’ strange appearance:

The theory of the existence of intelligent life on Mars may be likened to the atomic theory in chemistry in that in both we are led to the belief in units which we are alike unable to define. Both theories explain the facts in their respective fields and are the only theories that do, while as to what an atom may resemble we know as little as what a Martian may be like. But the behavior of chemic compounds points to the existence of atoms too small for us to see, and in the same way the aspect and behavior of the Martian markings implies the action of agents too far away to be made out.

Photos of Mars showing the canals were published in the December 1907 issue of The Century Magazine. Lowell wrote that

These little lines are the ‘canals’ which for their strange directness and yet stranger articulation were for long denied existence, and even now find a world slow to credit the story they have to tell. For it wounds man’s dignity to believe it. But to the camera no evasion of the fact avails.... That life is there is founded on no assumption, but on massed evidence that is conclusive, and the reader should realize that opposition to the idea that we now have proof of life on Mars is not based on reason, but on emotion....

Above at left are photographs of Mars (small) with a drawing (large) of the same area of Mars as shown in the photos, published by Percival Lowell in the December 1907 issue of The Century Magazine (the quality of this reproduction is not optimal). At right is a Century photograph of the expedition to the Chilean desert, where the skies are especially clear, to obtain the Mars photographs. Below are a 1907 photograph (left) and sketch (right) offered as evidence for the existence of Martian canals.

Above at left are photographs of Mars (small) with a drawing (large) of the same area of Mars as shown in the photos, published by Percival Lowell in the December 1907 issue of The Century Magazine (the quality of this reproduction is not optimal). At right is a Century photograph of the expedition to the Chilean desert, where the skies are especially clear, to obtain the Mars photographs. Below are a 1907 photograph (left) and sketch (right) offered as evidence for the existence of Martian canals.

And thus the Wall Street Journal’s article about proof of intelligent life on Mars. A newspaper reader in the nineteen-teens could find newspaper articles like the ones below, reporting on what the Martians were up to.

Left—article from the New York Times, August 27, 1911. The man at center is Lowell. Right—headline from the Portland Oregonian, February 15, 1910.

Left—article from the New York Times, August 27, 1911. The man at center is Lowell. Right—headline from the Portland Oregonian, February 15, 1910.

A 2006 Hubble Space Telescope photo of Mars: No canals.

A 2006 Hubble Space Telescope photo of Mars: No canals.

In the end, of course, this was all bogus. The canals and seas and oases turned out not to even exist—they were tricks of light and shadow and dust and rock. Modern photos of Mars show no such things. There is no intelligent life on Mars, nor in the solar system outside of Earth. There may well be no life at all in the solar system outside of Earth. Whewell was right. Flammarion, Schiaparelli, Lowell and the media who reported on the canals and the Martians were all wrong.

But for a span of some years, major media outlets were reporting that astronomers had finally found hard scientific evidence that intelligent life existed on another planet. So if you ever wondered what effect such a thing would have on society or religion or world peace, now you can find out—just see the effect the news had in the early twentieth century!

 

The Dark Energy Spectroscopic Instrument (DESI)
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This week there is a large gathering of extragalactic astronomers here at at Lawrence Berkeley National Lab (LBNL) to attend a conference on the Dark Energy Spectroscopic Instrument (DESI), a new experiment that will be commissioned on a large telescope on Kitt Peak National Observatory (KPNO) in Arizona.

With a team now 500 people strong, the focussed goal is to measure the relative positions and orientations of millions of galaxies in order to study properties of the early universe.

One can get at a straightforward understanding of this project by considering galaxy shapes. Galaxies are complicated objects with billions of stars. Even so, from a distance galaxies mostly take on oval shapes. These oval-shaped galaxies that we see on a typical pictures can face any which way. This turns out to be the case when one views galaxies within regions of space in which one can see only hundreds of examples at a time, but not millions.

On such scales indeed there is not any preferred order to their placement and orientation on the sky. Even so, when we consider now extending the image to include millions of galaxies, an interesting pattern emerges. Galaxies on very large scales start to form a dot-to-dot picture. Tracing the dots leads one to discover that galaxies are situated in a massive structure with thin filaments and the nodes that connect them similar to a 3D spider web.

We measure the average distances between these ‘strings’ of galaxies, similar in this analogy to measuring the average distances between the threads of a spider’s web. In this way, we are able to discern the conditions present in the early universe which led to this favored average distance being embedded into space itself. DESI will be mounted onto the 4-meter Mayall Telescope at KPNO in fall of this year.

An interfaith fellowship on religion and science
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It comes in the mail...

This might be very interesting to the readers of our blog... with Rabbi Geoff Mitelman's permission, I am posting here his email to me:

I'm writing to you because my organization, Sinai and Synapses, bridges the worlds of religion and science, and aims to elevate the public discourse in general. We have just opened applications for an interfaith Fellowship on religion and science, where we will bring together a select group of academics, clergy and writers for learning, networking and content creation in New York six times over two years. Through a generous grant, we will also be able to cover travel for all the meetings, (within North America).

We want to make sure we have a diverse collection of Fellows, so I wondered if you might know people who would be good candidates to apply, or even if you could share it in your networks.

Obviously, we can't promise anything, since we don't know how many applications we'll receive, and we will also have our own internal considerations as we balance scientific backgrounds, religious diversity, and gender balance in terms of whom we select. But I thought you would be a good person to reach out to in order to find some great potential candidates.

The link is below, and please let me know if you have any questions.

http://sinaiandsynapses.org/sinai-and-synapses-fellowship/

All good things,

Rabbi Geoff Mitelman

Kepler Team Releases Catalog with 219 new Exoplanet Candidates
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Artist's concept of a mini-planetary system. Image credit: NASA/JPL-Caltech

The story of the Kepler space telescope is a saga of discovery, heartbreak, and redemption. Launched in 2009, Kepler's mission was to search for Earth-size and smaller planets orbiting nearby stars, and to estimate how many stars in the Milky Way have such planets. Within the first few weeks of observations, five previously unknown exoplanets were found orbiting close to their parent star. Over the next few years, thousands of planetary candidates were discovered.

In July of 2012, one of the telescope's four reaction wheels failed; these are a type of flywheel that keep the spacecraft pointed at its target, and the telescope needs three to function properly. In May of 2013 a second reaction wheel failed, ending new data collection for the original mission and putting the continuation of the mission into jeopardy.

In November of 2013, a new mission plan dubbed K2 "Second Light" was devised - by balancing "light pressure" from the Sun on spacecraft's solar panels to act as a virtual reaction wheel, and using the two remaining working reaction wheels, the spacecraft would be able to continue collecting data. In early 2014 this method was successfully tested, and in March of 2014 data collection resumed.

The conception illustration depicts how solar pressure can be used to balance NASA's Kepler spacecraft, keeping the telescope stable enough to continue monitoring distant stars in search of transiting planets. Image credit: NASA Ames/W Stenzel

On June 19, 2017, the Kepler team announced the discovery of 50 potentially habitable planets orbiting nearby stars, and the unexpected statistic that smaller planets seem to fall into two distinct size categories: Earth/Super-Earth size, and mini-Neptunes.

The K2 mission is funded through the end of 2019; on-board fuel is expected to be depleted by that time. Data analysis will likely continue for quite some time.


Kepler Space Telescope. Credit: NASA Eyes on the Solar System / Bob Trembley

NASA/JPL Press Release 2017-168:
NASA's Kepler space telescope team has released a mission catalog of planet candidates that introduces 219 new candidates, 10 of which are near-Earth size and orbiting in their star's habitable zone, which is the range of distance from a star where liquid water could pool on the surface of a rocky planet.

This is the most comprehensive and detailed catalog release of candidate exoplanets, which are planets outside our solar system, from Kepler's first four years of data. It's also the final catalog from the spacecraft's view of the patch of sky in the Cygnus constellation.

With the release of this catalog, derived from data publicly available on the NASA Exoplanet Archive, there are now 4,034 planet candidates identified by Kepler. Of those, 2,335 have been verified as exoplanets. Of roughly 50 near-Earth size habitable zone candidates detected by Kepler, more than 30 have been verified.

Additionally, results using Kepler data suggest two distinct size groupings of small planets. Both results have significant implications for the search for life. The final Kepler catalog will serve as the foundation for more study to determine the prevalence and demographics of planets in the galaxy, while the discovery of the two distinct planetary populations shows that about half the planets we know of in the galaxy either have no surface, or lie beneath a deep, crushing atmosphere -- an environment unlikely to host life.

The findings were presented at a news conference Monday at NASA's Ames Research Center in California's Silicon Valley.

"The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs - planets with roughly the same size and orbit as Earth," said Mario Perez, Kepler program scientist in the Astrophysics Division of NASA's Science Mission Directorate. "Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth."

The Kepler space telescope hunts for planets by detecting the minuscule drop in a star's brightness that occurs when a planet crosses in front of it, called a transit.

This is the eighth release of the Kepler candidate catalog, gathered by reprocessing the entire set of data from Kepler's observations during the first four years of its primary mission. This data will enable scientists to determine what planetary populations -- from rocky bodies the size of Earth, to gas giants the size of Jupiter -- make up the galaxy's planetary demographics.

To ensure a lot of planets weren't missed, the team introduced their own simulated planet transit signals into the data set and determined how many were correctly identified as planets. Then, they added data that appear to come from a planet, but were actually false signals, and checked how often the analysis mistook these for planet candidates. This work told them which types of planets were overcounted and which were undercounted by the Kepler team's data processing methods.

"This carefully-measured catalog is the foundation for directly answering one of astronomy's most compelling questions - how many planets like our Earth are in the galaxy?" said Susan Thompson, Kepler research scientist for the SETI Institute in Mountain View, California, and lead author of the catalog study.

One research group took advantage of the Kepler data to make precise measurements of thousands of planets, revealing two distinct groups of small planets. The team found a clean division in the sizes of rocky, Earth-size planets and gaseous planets smaller than Neptune. Few planets were found between those groupings.

This diagram illustrates how planets are assembled and sorted into two distinct size classes. First, the rocky cores of planets are formed from smaller pieces. Then, the gravity of the planets attracts hydrogen and helium gas. Finally, the planets are "baked" by the starlight and lose some gas. At a certain mass threshold, planets retain the gas and become gaseous mini-Neptunes; below this threshold, the planets lose all their gas, becoming rocky super-Earths. Image credit: NASA/Ames Research Center/JPL-Caltech/R. Hurt

Using the W. M. Keck Observatory in Hawaii, the group measured the sizes of 1,300 stars in the Kepler field of view to determine the radii of 2,000 Kepler planets with exquisite precision.

"We like to think of this study as classifying planets in the same way that biologists identify new species of animals," said Benjamin Fulton, doctoral candidate at the University of Hawaii in Manoa, and lead author of the second study. "Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree."

It seems that nature commonly makes rocky planets up to about 75 percent bigger than Earth. For reasons scientists don't yet understand, about half of those planets take on a small amount of hydrogen and helium that dramatically swells their size, allowing them to "jump the gap" and join the population closer to Neptune's size.

The population of exoplanets detected by the Kepler mission (yellow dots) compared to those detected by other surveys using various methods: radial velocity (light blue dots), transit (pink dots), imaging (green dots), microlensing (dark blue dots), and pulsar timing (red dots). For reference, the horizontal lines mark the sizes of Jupiter, Neptune and Earth, all of which are displayed on the right side of the diagram. The colored ovals denote different types of planets: hot Jupiters (pink), cold gas giants (purple), ocean worlds and ice giants (blue), rocky planets (yellow), and lava worlds (green). The shaded gray triangle at the lower right marks the exoplanet frontier that will be explored by future exoplanet surveys. Kepler has discovered a remarkable quantity of exoplanets and significantly advanced the edge of the frontier. Image credit: NASA/Ames Research Center/Natalie Batalha/Wendy Stenzel

The Kepler spacecraft continues to make observations in new patches of sky in its extended mission, searching for planets and studying a variety of interesting astronomical objects, from distant star clusters to objects such as the TRAPPIST-1 system of seven Earth-size planets, closer to home.

Ames manages the Kepler missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

Highlighted are new planet candidates from the eighth Kepler planet candidate catalog that are less than twice the size of Earth and orbit in the stars' habitable zone – the range of distances from a star where liquid water could pool on the surface of an orbiting planet. The dark green area represents an optimistic estimate for the habitable zone, while the brighter green area represents a more conservative estimate for the habitable zone. The candidates are plotted as a function of their stars' surface temperature on the vertical axis and by the amount of energy the planet candidate receives from its host star on the horizontal axis. Brighter yellow circles show new planet candidates in the eighth catalog, while pale yellow circles show planet candidates from previous catalogs. Blue circles represent candidates that have been confirmed as planets due to follow-up observations. The sizes of the colored disks indicate the sizes of these exoplanets relative to one another and to the image of Earth, Venus and Mars, placed on this diagram for reference. Note that the new candidates tend to be around stars more similar to the sun – around 5,800 Kelvin – representing progress in finding planets that are similar to the Earth in size and temperature that orbit sun-like stars. Image credit: NASA/Ames Research Center/Wendy Stenzel

For more information about the Kepler mission, visit: https://www.nasa.gov/kepler

News Media Contacts

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Michele Johnson
Ames Research Center, California's Silicon Valley
650-604-6882
michele.johnson@nasa.gov


Further Reading:

Stellar Radiation Pressure: http://hyperphysics.phy-astr.gsu.edu/hbase/Starlog/staradpre.html
NASA Exoplanet Archive: https://exoplanetarchive.ipac.caltech.edu
Kepler Mission Homepage: https://www.nasa.gov/mission_pages/kepler/main/index.html
Kepler Mission on Wikipedia: https://en.wikipedia.org/wiki/Kepler_(spacecraft)
Educational Resources: https://www.nasa.gov/kepler/education
Citizen Science Projects: https://www.nasa.gov/kepler/education/citizen

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