Researchers at the University of Idaho say that Uranus, the distant gas giant known for being tipped by 90 degrees, might have two more moons than has previously been thought.
UI physics graduate student Robert O. Chancia and an assistant professor of physics at the university, Dr. Matthew M. Hedman, analyzed data obtained when Voyager 2 transmitted radio waves through Uranus’ rings.
They also looked at changes in the amount of light from distant stars that moves through the planet’s ring system.
Chancia and Hedman found that patterns in the distribution of ring material near the edges of Uranus’ alpha and beta rings vary over time, indicating that small moons may be present.
Dr. Richard G. French, a professor of astrophysics and director of the Whitin Observatory at Wellesley College in Massachusetts, said in an email message that the two UI scientists essentially used a meticulous process of comparison to determine that the pattern was caused by moons.
“Chancia and Hedman compared the wavelike properties from ring profiles taken at slightly different times and different geometries to work backwards to infer the properties of a nearby moon that might produce the satellite wakes,” he wrote.
Hedman pointed out that the results obtained when ground-based receiving stations interpreted the patterns of radio waves after they passed through the two rings shows that the waves were diffracted to varying degrees.
“When you look at this pattern in different places around the ring, the wavelength is different — that points to something changing as you go around the ring,” Hedman said. “There’s something breaking the symmetry.”
The researchers concluded that two possible small moonlets close to Uranus may be the culprits.
“We find for both rings that a moonlet located about 100 [kilometers] exterior to each ring could cause the optical depth variations seen in their occultation scans,” they write in the paper.
French explained that the proposed moons would be quite close to the alpha and beta rings.
“In this case, both moons are slightly exterior to the rings, so they orbit slightly more slowly than the rings themselves,” he wrote in an email message. “As the ring particles pass the moon, their orbits are slightly perturbed, resulting in a ripple pattern within the ring that is detectable as a periodic wavelike structure.”
Those “moonlet wakes” would help to maintain the structure of the Uranian rings, keeping them narrow. The rings are composed of a huge number of tiny particles, which eventually spread out as collisions between them occur.
Moons near the rings can limit that effect.
French used the example of the planet that may be the solar system’s most famous example of a ring system to explain that a phenomenon called resonance could account for the confining impact of small moons.
“If you are orbiting Saturn, for example, and you are a little ring particle and you orbit Saturn seven times and the little moon Prometheus six times in that same interval, that’s like getting pushed by the little finger on the swing,” he said. “That little push might be teeny but collectively is powerful. That’s kind of the notion that Matt and his student came up with. Those moons are in the right place to produce this wave pattern inside the rings.”
Chancia said in an email message that he and Hedman are not certain that such moonlet wakes occur in Uranus’ alpha and beta rings.
“We really just wanted to point it out as a possibility, because no one has come up with a universally accepted solution to how these rings are confined,” he wrote. “Anyway, the structures we found look like moonlet wakes.”
If they exist, the two moons would be Uranus’ smallest known and would have a diameter of four to 14 kilometers.
The proposed moons, if they are there, were not seen by Voyager 2’s cameras. One reason is that the moons are likely so small that the 1970s-vintage equipment could not detect them.
“[G]iven the small predicted sizes of the ∝ and ß moonlets, a convincing detection may not be possible in the Voyager 2 images,” wrote Chancia and Hedman in their paper.
The two newly-hypothesized Uranian moons may also have a very low albedo, which would make imaging of them difficult. Like the rings to which they are adjacent, they would not reflect much sunlight because the material from which they are constructed is not especially reflective.
“We know that the Uranian rings are dark because we can compare the amount of light they block during a stellar occultation – a measure of how much material there is in the rings – with how bright they are in reflected sunlight,” French wrote in an email.
“The answer is that they are quite dark – they are not composed of pure water ice, and it’s likely that they are darkened by dust contamination and perhaps by charged particles in the Uranian environment.”
French explained that the two moons proposed by Chancia and Hedman are likely to exhibit the same characteristic.
“If the satellites are dark, too, then they are stealth objects,” he said. “They are also bloody far away.”
Uranus has 27 known moons, all named for literary characters in William Shakespeare’s plays, and 13 rings that have widths between one and 100 kilometers.
The planet’s ring system was discovered in 1977 by ground-based observers using the Kuiper Airborne Observatory.
Voyager 2 was launched in 1977. Voyager 1, a twin outer solar system probe, was sent into space the same year. The latter has now left the solar system and Voyager 2 is likely to do so within the next few years.
Update, Oct. 26, 2017, 2:42 pm MDT: The word “part” was changed to the word “particle” in a quote by Professor Richard G. French in order to reflect the correct quotation.
NASA announced Monday that scientists using the Hubble Space Telescope have found evidence of water plumes on Europa, which means that spacecraft may be able to explore the moon’s ocean without the need to penetrate its icy surface.
A research team led by astronomer William Sparks of the Space Telescope Science Institute in Baltimore used a technique that has often been instrumental in discovering exoplanets to identify the plumes.
As an exoplanet moves in front of its star, the light from that star changes as it passes through the exoplanet’s atmosphere. This happens because the light encounters a variety of molecules.
On Europa, Sparks and his team noticed that the molecules in the moon’s atmosphere included water vapor. That led them to embark on a quest to determine whether water from Europa’s subsurface ocean is being expelled into space.
The scientists observed Europa pass in front of Jupiter, from which the Sun’s light would be reflected through the atmosphere of the Jovian moon, ten times in 15 months. On three of the occasions water vapor was detected.
“This is an exciting find because it potentially gives us access to the ocean below,” Sparks said at a NASA teleconference on Monday.
Scientists are interested in sampling Europa’s ocean because it may provide indications of whether the moon is, or ever has been, hospitable to life.
“On Earth, life is found wherever there is energy, water, and nutrients, so we have a special interest in any place that has those characteristics,” Dr. Paul Hertz, director of NASA’s astrophysics division in Washington, D.C., said. “Europa might be such a place.”
Europa has a large sub-surface ocean that is thought to contain more water than all of the oceans on Earth. However, the satellite also has a thick icy crust atop that ocean.
The water plumes may rise as high as 200 kilometers off Europa’s surface.
“Europa’s ocean is considered to be one of the most promising places that could potentially harbor life in the solar system,” Geoff Yoder, the acting associate administrator for NASA’s Science Mission Directorate, said. “These plumes, if they do indeed exist, may provide another way to sample Europa’s subsurface.”
A team led by Lorenz Roth of the Southwest Research Institute in Austin, Tex. identified water plumes rising from Europa’s south pole once during 2012.
The Roth group used the Hubble Space Telescope’s Imaging Spectrograph to identify hydrogen and oxygen ions by the ultraviolet radiation they emit after particles accelerated by Jupiter’s magnetic field split water molecules in the Europan atmosphere.
The STScI group also used the STIS instrument, but instead obtained imagery of Europa’s atmosphere in ultraviolet light.
“It’s a technique that complements the Roth team’s,” Dr. Jennifer J. Wiseman, an astrophysicist at NASA’s Goddard Space Flight Center and the agency’s senior scientist assigned to the Hubble Space Telescope, said.
Wiseman explained that STIS’ ultraviolet imaging capacity was particularly helpful to the STScI researchers.
“In ultraviolet light, the surface of Jupiter looks more uniform in color than in visible light, so that allowed the Sparks team to more clearly see the silhouette image of the possible plumes on Europa as the moon passed in front of the smooth Jupiter background,” she wrote in an email message.
The Roth team also used STIS during their quest for Europa’s plumes in 2012.
Sparks said that, notwithstanding a different methodology of investigation, the STScI results are similar to those found by Roth and his colleagues.
“When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it’s pretty similar to what Roth and his team found,” he explained. “The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work.”
The STScI and Roth teams have not seen plumes erupting from Europa at the same times. Sparks and his colleagues observed what they believe to be water plumes in January, March, and April, 2014.
Wiseman said that detection of Europa’s plumes is difficult.
“Such plumes would be faint, probably intermittent, and the ultraviolet wavelengths of light being observed are at the high frequency edge of what Hubble can detect,” she wrote in an email message.
Sparks explained that he and his team do not claim that their work proves the plumes’ existence, though he also said Monday that he does not believe that any other explanation for the findings his team made is likely.
“In a formal sense, we have a statistically significant result,” Sparks said. “The problem is that there may be something we don’t understand about the instrument or the scene. It’s more of a subjective uncertainty than a quantitative uncertainty.”
“I’m not aware of any other plausible natural explanation for the appearance of these patches of absorption,” he continued.
Two of the water plumes that were apparently observed by Sparks and his team occurred near the south pole of Europa and one was seen near the moon’s equator.
A paper detailing the findings by the STScI team will be published in the Sept. 29 edition of Astrophysical Journal.
Saturn’s moon Enceladus is the only body in the solar system known to eject water vapor to space.
Wiseman said during Monday’s teleconference that NASA plans to use the James Webb Space Telescope, due to be launched in 2018, to further investigate the possible water plumes of Europa.
NOTE 1: This post was updated at 5:38 pm MDT on Sept. 27, 2016 to add a discussion of Dr. Jennifer Wiseman’s interview responses.
NOTE 2: This post was updated at 9:32 pm MDT on Sept. 27, 2016 to correct an inaccurate statement contained in the headline, correct several minor errors in the quotation of Dr. Jennifer Wiseman’s email communication, and correct the acronym applicable to the Space Telescope Science Institute.
NOTE 3: This post was updated at 9:37 pm MDT on Sept. 27, 2016 to clarify the difference between the Roth team’s use of the Hubble Space Telescope’s Imaging Spectrograph in 2012 and the STScI team’s use of that instrument in 2014.
Today’s summer solstice in the northern hemisphere does not bring only the longest day of the year. Night sky watchers also have the opportunity to see, for the first time in 49 years, a full moon on the first day of summer.
The full moon occurs about once each month. The lunar year – the amount of time it takes for the moon to cycle through 12 lunar cycles – is 354 days; the lunar cycle averages 29.53 days.
A full moon occurs when the sun, Earth, and the moon are nearly aligned. During most full moons we see nearly all of one of the Moon’s hemispheres from our planet. We do not see all of that hemisphere during a typical full moon because, if we did, the sun, Earth, and moon would be so aligned as to result in a lunar eclipse.
The other hemisphere of the moon is never visible from Earth because the moon’s rate of rotation is equal to the amount of time it takes to orbit our planet.
Because tonight’s full moon occurs in June, it is colloquially known as a “strawberry moon.” According to the 1918 book The American Boy’s Book of Signs, Signals and Symbols, the nickname originated with native Americans of the northeastern United States because June is the month in which strawberries were harvested.
According to a 2012 National Geographic article, “Europeans have dubbed [a June full moon] the rose moon, while other cultures named it the hot moon for the beginning of the summer heat.”
The summer solstice in the northern hemisphere is the one day of the year on which the sun will be directly overhead at noon at the Tropic of Cancer. The sun is never directly overhead at a latitude north of the Tropic of Cancer or south of the Tropic of Capricorn.
In Colorado and the rest of the Mountain Time Zone of North America, the sun will get to its annual highest point in the sky at 4:34 pm.
The sun is directly overhead at high noon above the Tropic of Capricorn on the winter solstice in the northern hemisphere.
The southern hemisphere experiences its summer solstice on that day and its winter solstice when the sun is directly overhead at the Tropic of Cancer.
CORRECTION, June 20, 2016, 5:24 pm MDT: This article originally stated that the last summer solstice full moon occurred in 1949, 67 years ago. That is not an accurate statement and the article has been edited to correct the error.
Makemake, a dwarf planet far beyond Pluto in the Kuiper Belt, has a moon.
Imagery obtained by the Hubble Space Telescope detected the satellite last April, according to a recently published paper.
The moon, which has been temporarily catalogued as S/2015 (136472) 1 and nicknamed MK2, is about 100 miles in diameter. It was observed orbiting Makemake from a distance of about 13,000 miles.
MK2 probably orbits Makemake in an orientation that makes it difficult for astronomers to observe the moon.
“Our preliminary estimates show that the moon’s orbit seems to be edge-on, and that means that often when you look at the system you are going to miss the moon because it gets lost in the bright glare of Makemake,” Dr. Alex H. Parker, a planetary scientist at Southwest Research Institute in Boulder, Colo., said.
Parker led the team that analyzed the Hubble image of MK2.
One implication of the Makemakean moon’s discovery is an increased ability to measure Makemake’s mass and density.
To measure the dwarf planet’s mass, scientists will need to overcome the challenges inherent in observing MK2’s orbit. If they succeed in doing so, and because the distance from Earth to Makemake is already known, it would be possible to use the orbital period and the mean distance of MK2 from Makemake to determine Makemake’s mass.
To determine Makemake’s density, scientists must know its volume, which in turn requires knowledge of the dwarf planet’s diameter. Makemake’s diameter is about 1,500 kilometers.
Once the volume is determined, density can be calculated by dividing Makemake’s mass by its volume.
Astronomers used a camera on the Hubble Space Telescope to find MK2. That instrument, called Widefield Camera 3, is able to capture images across the radiation spectrum.
Widefield Camera 3 has a 16 megapixel capacity and can capture an image as large as 160 arcseconds by 160 arcseconds in size.
Makemake is the second-brightest object, after Pluto, in the Kuiper Belt and is, like Pluto, covered with methane ice.
The dwarf planet, which was discovered in 2005, is named for a deity that is worshiped by native people of Easter Island.
In addition to Makemake, there are four other dwarf planets in the solar system: Pluto, Eris, Haumea, and Ceres.
With the discovery of MK2, astronomers now know that all of the solar system’s dwarf planets have moons.
Scientists have found a planet about the size of Jupiter orbiting two stars in a nearby solar system, marking the largest known example of a world with multiple suns.
The circumbinary planet, which has been named Kepler-1647b, is in the constellation Cygnus, about 3,700 light years from Earth. Astronomers used the Kepler Space Telescope to discover it.
“It’s a bit curious that this biggest planet took so long to confirm, since it is easier to find big planets than small ones,” Dr. Jerome A. Orosz, an astronomer at San Diego State University and a co-author of a paper documenting the discovery, said. “But it is because its orbital period is so long.”
Kepler-1647b’s orbital period is 1,107 days, which means it takes longer to orbit its stars than any other known exoplanet takes to orbit either one star or two.
The planet’s circumbinary orbit made it more difficult to find than would be the case with an exoplanet that circles one star.
“The transits are not regularly spaced in time and they can vary in duration and even depth,” Dr. William F. Welsh, another SDSU astronomer and co-author of the paper explaining the discovery, said.
A gas giant, Kepler-1647b is has a similar age as Earth – about 4.4 billion years. The two stars it orbits are similar to our sun, with one being a little larger than the Sun and the other slightly smaller than Earth’s star.
The discovery of Kepler-1647b is described in a paper to be published in Astrophysical Journal.
Astronomers have discovered three exoplanets in a nearby star system that may be comparable to the size of Earth and Venus and one of them may also be located at distance from its star to experience temperatures similar to our planet.
The planets are about 40 light years from our planet and orbit a dwarf star that is about one-eighth the size of our sun, or approximately the size of Jupiter. The dwarf star, which astronomers consider to be “ultracool,” is so much cooler than our sun that the system’s habitable zone is much closer to it than in our solar system.
A star’s habitable zone is the area of its star system in which temperatures may be hospitable to environmental conditions amenable to life.
Two of the exoplanets have orbital periods of less than three days; they probably receive two-to four times the amount of solar radiation that Earth does.
The third and most distant of the exoplanets experiences a year that is at least four and as many as 73 days long.
“These planets are so close, and their star so small, we can study their atmosphere and composition, and further down the road, which is within our generation, assess if they are actually inhabited,” Julien de Wit, a postdoctoral researcher at Massachusetts Institute of Technology and a co-author of the paper announcing the discovery, said.
The two exoplanets closest to their star are likely tidally locked to it, meaning that one side of the planet always faces the star. Those two planets are generally too hot on their day-sides, and too cold on their night sides, to support life, though the team of scientists that published the paper describing them said that there may be small areas on their western hemispheres that might be temperate enough to do so.
The third planet from the star could be in its habitable zone, meaning liquid water could occur on its surface.
The three exoplanets are the first ever discovered orbiting an ultracool dwarf star.
Researchers used the TRAPPIST instrument in Chile to find the exoplanets. Because their star emits so little radiation, compared to larger stars, it cannot be seen with an optical telescope.
TRAPPIST, which is an acronym for TRAnsiting Planets and PlanetesImals Small Telescope, detects radiation in the infrared band of the spectrum. Starting in September 2015 the scientists periodically detected a lessening of the amount of the star’s infrared radiation detected by the instrument. That indicated the likelihood that several objects were passing in front of it.
The paper describing the discovery of the exoplanets was published online in the May 12 edition of Nature.
Video courtesy NASA
This month provides an opportunity to see a meteor shower and three planets in the night sky.
The highlight will continue to be the chance to see Jupiter, which will shine brightly after being at opposition on March 8. Look to the south-southeast in the early evening, just after twilight; the solar system’s largest planet is in the constellation Leo. On April 17 you can see it moving with the waxing gibbous moon.
Mercury will become visible on April 8 as a fairly bright object with a -1 magnitude. The closest planet to the Sun passed its perihelion on April 5 and can be seen low in the western sky about 30 or 40 minutes after sunset. By April 18 Mercury will become quite a bit less bright, though it will be about 20 degrees east of the Sun by then. That makes it easier to see because it will be higher in the sky and will take longer to set. Whenever you observe the meteor shower, try to find a location away from any artificial lights.
You can best see Mars on or about April 24, when it reaches a magnitude of about -1.2 to -1.4. It will appear below the waxing gibbous moon as a yellowish-orange object. Look to the constellation Opheuchus to find Mars.
The Lyrid meteor shower peaks before dawn on April 22, but its annual visit corresponds with a full moon. However, the meteor shower starts on April 16, which might allow for some visibility of objects falling through the atmosphere before the full moon arrives.