Each image in a pair was taken two weeks apart. He then placed both images of each section in a machine called a blink comparator , which by exchanging images quickly created a time lapse illusion of the movement of any planetary body. To reduce the chances that a faster-moving and thus closer object be mistaken for the new planet, Tombaugh imaged each region near its opposition point, degrees from the Sun, where the apparent retrograde motion for objects beyond Earth's orbit is at its strongest.
He also took a third image as a control to eliminate any false results caused by defects in an individual plate. Tombaugh decided to image the entire zodiac, rather than focus on those regions suggested by Lowell.
By the beginning of , Tombaugh's search had reached the constellation of Gemini. On 18 February , after searching for nearly a year and examining nearly 2 million stars, Tombaugh discovered a moving object on photographic plates taken on 23 January and 29 January of that year.
The new object was later precovered on photographs dating back to 19 March He found hundreds of variable stars and asteroids , as well as two comets , but no further planets.
To the observatory's disappointment and surprise, Pluto showed no visible disc; it appeared as a point, no different from a star, and, at only 15th magnitude, was six times dimmer than Lowell had predicted, which meant it was either very small, or very dark. Almost immediately, some astronomers questioned Pluto's status as a planet. Leuschner suggested that Pluto's dimness and high orbital eccentricity made it more similar to an asteroid or comet: "The Lowell result confirms the possible high eccentricity announced by us on April 5.
Among the possibilities are a large asteroid greatly disturbed in its orbit by close approach to a major planet such as Jupiter, or it may be one of many long-period planetary objects yet to be discovered, or a bright cometary object.
Brown asserted in agreement with E. Bower , that the presumed irregularities in the orbit of Uranus could not be due to the gravitational effect of a more distant planet, and thus that Lowell's supposed prediction was "purely accidental".
Throughout the midth century, estimates of Pluto's mass were revised downward. In , Nicholson and Mayall calculated its mass, based on its supposed effect on the giant planets, as roughly that of Earth; [31] a value somewhat in accord with the 0.
Wylie at the US Naval Observatory , using the same assumptions. In , Dennis Rawlins conjectured, based on the similarities in the periodicity and amplitude of brightness variation between Pluto and Neptune's moon Triton , that Pluto's mass must be similar to Triton's. This is, in fact, true, and had been argued by astronomers Walter Baade and E. Bower as early as It was nonetheless a meagre enough value for him to conclude that Pluto was not Planet X.
This meant that Pluto, far from being dark, was in fact exceptionally bright, and thus was probably no more than 0. Pluto's size was finally determined conclusively in , when American astronomer James W. Christy discovered its moon Charon. This enabled him, together with Robert Sutton Harrington of the U. Naval Observatory, to measure the mass of the Pluto—Charon system directly by observing the moon's orbital motion around Pluto. Lowell's "prediction" had been a coincidence: If there was a Planet X, it was not Pluto.
After , a number of astronomers kept up the search for Lowell's Planet X, convinced that, because Pluto was no longer a viable candidate, an unseen tenth planet must have been perturbing the outer planets. In the s and s, Robert Harrington led a search to determine the real cause of the apparent irregularities. Noted Planet X sceptic Brian G. Marsden of the Minor Planet Center pointed out that these discrepancies were a hundredth the size of those noticed by Le Verrier, and could easily be due to observational error.
Brady claimed that they could have been caused by a Jupiter-sized planet beyond Neptune at 59 AU that is in a retrograde orbit around the Sun. Kenneth Seidelmann attacked the hypothesis, showing that Halley's Comet randomly and irregularly ejects jets of material, causing changes to its own orbital trajectory, and that such a massive object as Brady's Planet X would have severely affected the orbits of known outer planets.
Although its mission did not involve a search for Planet X, the IRAS space observatory made headlines briefly in due to an "unknown object" that was at first described as "possibly as large as the giant planet Jupiter and possibly so close to Earth that it would be part of this Solar System".
In , A. Jackson and R. Killen studied the stability of Pluto's resonance with Neptune by placing test "Planet X-es" with various masses and at various distances from Pluto. Pluto and Neptune's orbits are in a resonance, which prevents their collision or even any close approaches, regardless of their separation in the z axis. It was found that the hypothetical object's mass had to exceed 5 Earth masses to break the resonance, and the parameter space is quite large and a large variety of objects could have existed beyond Pluto without disturbing the resonance.
Four test orbits of a trans-Plutonian planet have been integrated forward for four million years in order to determine the effects of such a body on the stability of the Neptune—Pluto resonance. Planets beyond Pluto with masses of 0. Test planets of 5 Earth masses with semi-major axes of Harrington died in January , without having found Planet X. Myles Standish had used data from Voyager 2 's flyby of Neptune, which had revised the planet's total mass downward by 0.
Template:TNO imagemap. Most are now recognized as part of the Kuiper belt , a swarm of icy bodies left over from the Solar System's formation that orbit near the ecliptic plane just beyond Neptune.
Though none were as large as Pluto, some of these distant trans-Neptunian objects, such as Sedna , were initially described in the media as "new planets". In , astronomer Mike Brown and his team announced the discovery of Template:Mp later named Template:Dp after the Greek goddess of discord and strife , a trans-Neptunian object then thought to be just barely larger than Pluto. Eris was never officially classified as a planet, and the definition of planet defined both Eris and Pluto not as planets but as dwarf planets because they have not cleared their neighbourhoods.
Pluto itself is now recognized as being a member of the Kuiper belt and the largest dwarf planet, larger than the more-massive Eris. Although most astronomers accept that Lowell's Planet X does not exist, a number have revived the idea that a large unseen planet could create observable gravitational effects in the outer Solar System.
These hypothetical objects are often referred to as "Planet X", although the conception of these objects may differ considerably from that proposed by Lowell.
The orbit of Sedna red set against the orbits of Jupiter orange , Saturn yellow , Uranus green , Neptune blue , and Pluto purple. When Sedna was discovered, its extreme orbit raised questions about its origin. Its perihelion is so distant approximately 75 AU that no currently observed mechanism can explain Sedna's eccentric distant orbit. It is too far from the planets to have been affected by the gravity of Neptune or the other giant planets and too bound to the Sun to be affected by outside forces such as the galactic tides.
Hypotheses to explain its orbit include that it was affected by a passing star, that it was captured from another planetary system , or that it was tugged into its current position by a trans-Neptunian planet. If Sedna had been pulled into its orbit by a trans-Neptunian planet, any other objects found in its region would have a similar perihelion to Sedna around 80 AU.
In , Rodney Gomes modelled the orbits of 92 Kuiper belt objects and found that six of those orbits were far more elongated than the model predicted. He concluded that the simplest explanation was the gravitational pull of a distant planetary companion, such as a Neptune-sized object at AU or a Mars-sized object at around 53 AU. In , astronomers announced the discovery of Template:Mpl , a large object with a Sedna-like year orbit and a perihelion of roughly 80 AU, [7] which led them to suggest that it offered evidence of a potential trans-Neptunian planet.
In astronomers at the Universidad Complutense in Madrid suggested that the available data actually indicate more than one trans-Neptunian planet. Even without gravitational evidence, Mike Brown, the discoverer of Sedna, has argued that Sedna's 12,year orbit means that probability alone suggests that an Earth-sized object exists beyond Neptune.
The thing that is so astonishing about these orbits is how they came to be like this, and how oddly similar they are in their approach to the Sun. Ultimately, it is believed that such revolutions can only happen if there is something massive that impacts their orbits. But as far as astronomers know, there are no massive objects close enough to the two dwarf planets to do that.
This orbit raised the possibility that there is an unknown planet in the outer solar system that pulls these two dwarfs outward. To confirm this, the astronomers that discovered VP observed the Kuiper Belt more intently, and they saw that 10 more objects followed the same orbit. For the astronomers, this is more than a mere coincidence. They suspect that there is something that causes the planets to be pulled out of the plane in this very similar manner, so they say that this find only strengthens the case for an undiscovered planet.
Ultimately, Trujillo and Sheppard estimated that there is an undiscovered planet very far out of the solar system astronomical units, or eight times as far from the Sun as Neptune.
However, this is not the only possibility. Trujillo and Sheppard also note that a closer, and less massive planet, could also impact these objects in this way.
Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help. Environment COP26 nears conclusion with mixed signals and frustration. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries. History Magazine These 3,year-old giants watched over the cemeteries of Sardinia.
Science Coronavirus Coverage What families can do now that kids are getting the vaccine. Magazine How one image captures 21 hours of a volcanic eruption. Science Why it's so hard to treat pain in infants. Science The controversial sale of 'Big John,' the world's largest Triceratops.
Science Coronavirus Coverage How antivirals may change the course of the pandemic. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. Subscriber Exclusive Content. Why are people so dang obsessed with Mars? How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history.
0コメント