question: why do comets take a sharp turn near the sun instead of continuing past it a longer distance that's more equal to their voyage toward the sun?
comment: The main issue is how much angular momentum they have with respect to the sun (or other body being orbiter). Starting from a great distance away they have time to accelerate a lot toward the sun from its gravity, but they don't have the momentum to the side to form a roughly circular orbit like the planets do. As they get in close to the sun the angle of the sun's gravity starts to change and the relatively greater force of gravity pulls their path around, pointing their momentum from falling toward the sun into pointing away from it. Then it coasts outward being slowed by gravity until it falls back in.
passages: Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands of years. An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System. For example, Comet McNaught had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage epoch in January 2007 but is bound to the Sun with roughly a 92,600-year orbit because the eccentricity drops below 1 as it moves farther from the Sun. The future orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. By definition long-period comets remain gravitationally bound to the Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as Comet West and C/1999 F1 can have aphelion distances of nearly 70,000 AU with orbital periods estimated around 6 million years.
   Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further gravitational perturbations. Short-period comets have a tendency for their aphelia to coincide with a giant planet's semi-major axis, with the JFCs being the largest group. It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by the gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined. These perturbations can deflect long-period comets into shorter orbital periods.
   Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/scattered disc —a disk of objects in the trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesised its existence). Vast swarms of comet-like bodies are thought to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper belt objects) or nearby stars (in the case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards toward the Sun to form a visible comet. Unlike the return of periodic comets, whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable.
   Most comets are small Solar System bodies with elongated elliptical orbits that take them close to the Sun for a part of their orbit and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital periods: The longer the period the more elongated the ellipse.
  
  Section::::Orbital characteristics.:Short period.
   Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.
   The comet is thought to be a member of a relatively new class of objects called "centaurs", of which at least 400 are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that centaurs are recent escapees from the Kuiper belt, a zone of small bodies orbiting in a cloud at the distant reaches of the Solar System. Frequent perturbations by Jupiter will likely accumulate and cause the comet to migrate either inward or outward by the year 4000.
   Over many orbits, the cumulative effect of gravitational perturbations on comets with high orbital inclinations and small perihelion distances is generally to reduce the perihelion distance to very small values. Hale–Bopp has about a 15% chance of eventually becoming a sungrazing comet through this process.
  
  Section::::Scientific results.
   The first observations were made in the 1980s and 90s as several spacecraft flew by comets 21P/Giacobini–Zinner, 1P/Halley, and 26P/Grigg–Skjellerup. It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at, for example, Earth. These observations were all made near perihelion when the bow shocks already were fully developed.
   Section::::Causes.:Size and activity of the nucleus.
  
  Cometary nuclei vary in size from a few hundreds of metres across or less to many kilometres across. When they approach the Sun, large amounts of gas and dust are ejected by cometary nuclei, due to solar heating. A crucial factor in how bright a comet becomes is how large and how active its nucleus is. After many returns to the inner Solar System, cometary nuclei become depleted in volatile materials and thus are much less bright than comets which are making their first passage through the Solar System.
   The brightness of a simple reflective body varies with the inverse square of its distance from the Sun. That is, if an object's distance from the Sun is halved, its brightness is quadrupled. However, comets behave differently, due to their ejection of large amounts of volatile gas which then also reflect sunlight and may also fluoresce. Their brightness varies roughly as the inverse cube of their distance from the Sun, meaning that if a comet's distance from the Sun is halved, it will become eight times as bright.
   Due to the Sun's gravitational pull, a spacecraft moving farther from the Sun will slow down, while a spacecraft moving closer will speed up. Also, since any two planets are at different distances from the Sun, the planet from which the spacecraft starts is moving around the Sun at a different speed than the planet to which the spacecraft is travelling (in accordance with Kepler's Third Law). Because of these facts, a spacecraft desiring to transfer to a planet closer to the Sun must decrease its speed with respect to the Sun by a large amount in order to intercept it, while a spacecraft traveling to a planet farther out from the Sun must increase its speed substantially. Then, if additionally the spacecraft wishes to enter into orbit around the destination planet (instead of just flying by it), it must match the planet's orbital speed around the Sun, usually requiring another large velocity change.
   In the Solar System, planets, asteroids, most comets and some pieces of space debris have approximately elliptical orbits around the Sun. Strictly speaking, both bodies revolve around the same focus of the ellipse, the one closer to the more massive body, but when one body is significantly more massive, such as the sun in relation to the earth, the focus may be contained within the larger massing body, and thus the smaller is said to revolve around it. The following chart of the perihelion and aphelion of the planets, dwarf planets and Halley's Comet demonstrates the variation of the eccentricity of their elliptical orbits. For similar distances from the sun, wider bars denote greater eccentricity. Note the almost-zero eccentricity of Earth and Venus compared to the enormous eccentricity of Halley's Comet and Eris.
   , only 20 comets have been observed to pass within of Earth, including 10 which are or have been short-period comets. Two of these comets, Halley's Comet and 73P/Schwassmann–Wachmann, have been observed during multiple close approaches. The closest observed approach was 0.0151 AU (5.88 LD) for Lexell's Comet on July 1, 1770. After an orbit change due to a close approach of Jupiter in 1779, this object is no longer a NEC. The closest approach ever observed for a current short-period NEC is 0.0229 AU (8.92 LD) for Comet Tempel–Tuttle in 1366. This comet is the parent body of the Leonid meteor shower, which also produced the Great Meteor Storm of 1833. Orbital calculations show that P/1999 J6 (SOHO), a faint sungrazing comet and confirmed short-period NEC observed only during its close approaches to the Sun, passed Earth undetected at a distance of 0.0121 AU (4.70 LD) on June 12, 1999.
   BULLET::::- If the specific orbital energy is positive the orbit is open, following a hyperbola with the larger body the focus of the hyperbola. Objects in open orbits do not return; once past periapsis their distance from the focus increases without bound. See radial hyperbolic trajectory
  
  BULLET::::- If the specific orbital energy is zero, (K.E = −P.E.): the orbit is a parabola with focus at the other body. See radial parabolic trajectory. Parabolic orbits are also open.
   Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. If comets pervaded interstellar space, they would be moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). If such objects entered the Solar System, they would have positive specific orbital energy and would be observed to have genuinely hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century within Jupiter's orbit, give or take one and perhaps two orders of magnitude.
   The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the solar system. Using JPL Horizons, the barycentric orbital elements for epoch 2020-Jan-01 generate a semi-major axis of 1,100 AU, an apoapsis distance of 2,230 AU, and a period of approximately 37,000 years.
  
  Section::::External links.
  
  BULLET::::- Surf the Web to see the Sun-dancing comet (ESA 2003-Feb-12)
  
  BULLET::::- Comet Neat Passes an Erupting Sun (APOD 2003 February 24)
   Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are thought to originate in the Kuiper belt, whereas long-period comets, such as Hale–Bopp, are thought to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent. Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult. Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.
  
  Section::::Trans-Neptunian region.
   Periodic comets or short-period comets are generally defined as those having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets (Jupiter and beyond) at aphelion; for example, the aphelion of Halley's Comet is a little beyond the orbit of Neptune. Comets whose aphelia are near a major planet's orbit are called its "family". Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits.
   Asteroids can become ejected or in a highly eccentric orbit around the Sun by being ejected by planets like Jupiter. Just because an orbit solution looks unbound at an epoch when the object is near perihelion (closest approach to the Sun) does not mean the orbit will be unbound when beyond the planets.
  
  Section::::See also.
  
  BULLET::::- ʻOumuamua, formerly designated a hyperbolic asteroid, but may be an exocomet instead.
  
  BULLET::::- Hyperbolic comet, a Solar System comet with an eccentricity greater than 1.
  
  BULLET::::- Interstellar object, an object arriving from outside the Solar System. Those objects usually have unbound (e1) orbits.
   Comets have very different values of eccentricity. Periodic comets have eccentricities mostly between 0.2 and 0.7, but some of them have highly eccentric elliptical orbits with eccentricities just below 1, for example, Halley's Comet has a value of 0.967. Non-periodic comets follow near-parabolic orbits and thus have eccentricities even closer to 1. Examples include Comet Hale–Bopp with a value of 0.995 and comet C/2006 P1 (McNaught) with a value of . As Hale–Bopp's value is less than 1, its orbit is elliptical and it will return. Comet McNaught has a hyperbolic orbit while within the influence of the planets, but is still bound to the Sun with an orbital period of about 10 years. As of a 2010 Epoch, Comet C/1980 E1 has the largest eccentricity of any known hyperbolic comet with an eccentricity of 1.057, and will leave the Solar System eventually.
   Section::::Origin of sungrazing comets.
  
  Studies show that for comets with high orbital inclinations and perihelion distances of less than about 2 astronomical units, the cumulative effect of gravitational perturbations over many orbits is adequate to reduce the perihelion distance to very small values. One study has suggested that Comet Hale–Bopp has about a 15% chance of eventually becoming a sungrazer.
  
  Section::::Role in solar astronomy.
  
  The motion of tails of sungrazers that survive perihelion (such as Comet Lovejoy) can provide solar astronomers with information about the structure of the solar corona, particularly the detailed magnetic structure.
  
  Section::::See also.
  
  BULLET::::- Helion (meteoroid)
   Single-apparition or non-periodic comets are similar to long-period comets because they also have parabolic or slightly hyperbolic trajectories when near perihelion in the inner Solar System. However, gravitational perturbations from giant planets cause their orbits to change. Single-apparition comets have a hyperbolic or parabolic osculating orbit which allows them to permanently exit the Solar System after a single pass of the Sun. The Sun's Hill sphere has an unstable maximum boundary of 230,000 AU (). Only a few hundred comets have been seen to reach a hyperbolic orbit (e  1) when near perihelion that using a heliocentric unperturbed two-body best-fit suggests they may escape the Solar System.
   Section::::Fate of comets.
  
  Section::::Fate of comets.:Departure (ejection) from Solar System.
  
  If a comet is traveling fast enough, it may leave the Solar System. Such comets follow the open path of a hyperbola, and as such they are called hyperbolic comets. To date, comets are only known to be ejected by interacting with another object in the Solar System, such as Jupiter. An example of this is thought to be Comet C/1980 E1, which was shifted from a predicted orbit of 7.1 million years around the Sun, to a hyperbolic trajectory, after a 1980 close pass by the planet Jupiter.
   BULLET::::- Planetary rotation and atmospheric phenomena: In "Letters on Sunspots" Galileo claimed that sunspots were similar to clouds on Earth, carried around by the rotation of the Sun. In contrast, in "Discourse on Comets" Galileo conjectured that the atmospheric conditions that might produce comets as an optical effect were static and were not carried round by the Earth's motion.
   Many near-parabolic comets are much further from the Sun. Caesar's Comet (C/-43 K1) is calculated to be more than from the Sun. Comet Donati (C/1858 L1) is from the Sun.
  
  Section::::See also.
  
  BULLET::::- List of possible dwarf planets
  
  BULLET::::- List of Solar System objects by greatest aphelion
  
  BULLET::::- List of most distant trans-Neptunian objects
  
  BULLET::::- List of Solar System objects most distant from the Sun in 2018
  
  BULLET::::- List of trans-Neptunian objects
  
  BULLET::::- V774104, another very distant object found by the same team
  
  BULLET::::- 2018 VG18, the next most distant object discovered in 2018, nicknamed "FarOut"
  
  Section::::External links.
  