Download This Month In Astronomy - Astronomy Club of Virginia Tech

This Month In Astronomy
Monthly updates related to astronomy, brought to you by Astronomy Club of Virginia Tech
Nov, 2015
● Kuiper Belt, Scattered Disk, and Oort Cloud
Recently, with the fly-by mission of New Horizons snapping and delivering shots for Pluto, interests were reignited for this icy dwarf planet. While it was fascinating to see Pluto being unveiled for the first time in closeups, it is important to realize that Pluto is just one of the many, many Trans-Neptunian objects. There are three
major categories of Trans-Neptunian objects, understanding the distinctions between the three has given the
scientists more insights as to the origin and the future of the solar system.
The first category is Kuiper Belt Objects (KBOs). Our familiar Pluto and its moons belong to this
category. Kuiper Belt Objects extends from about 30 Astronomical Units (AU), where Neptune lies, to roughly 50
AU. KBOs primarily consists of icy rocks made of methane, ammonia, water. Even though Kuiper Belt has a
“belt” in its name, its actual shape was more like a “donut”. This is because that orbital inclinations of a fraction
of the KBOs are large enough that they fly out of the plane of eight planets in the solar system, as shown in the
plot below. The vertical axis is the degrees of inclination. A small number of KBOs have degrees of inclination
around 20 to 40 degrees, giving the Kuiper Belt the “donut” shape. Because Kuiper Belt objects are close to
Neptune, Neptune’s gravitational influence plays a significant influence on the orbits of this KBOs. Based on
their relationship with Neptune, KBOs can be divided into two sub-categories: classical KBOs and resonant
KBOs. Resonant KBOs have orbital periods that are exact ratios of Neptune’s. Because their motions are
synchronized with that of Neptune’s, they avoid being perturbed by the strong influence of Neptunian gravity.
Pluto belongs to resonant KBOs and is in 2:3 motion resonance with Neptune. Classical KBOs are found at 42
to 48 AUs and are between 2:3 to 1:2 resonance with Neptune. In this area, Neptune’s influence is negligible,
and thus the orbits of classical KBOs are stable.
Locations of some Trans-Neptunian objects and their inclinations with respect to the plane of planets. Kuiper
Belt objects are in blue, Scattered disk objects are in gray. Plutinos are a special kind of Kuiper Belt objects, and
are in red.
The second category is the scattered disk. The scattered disk objects are colored in gray in the plot
above. These objects fell into this category due to their further distance from the Sun (from around 47 AU to, for
some, 100 AU), and their extreme inclination when compared to the plane of planets. Despite being further away
from Neptune, the orbital status of these scattered disk objects resulted in unstable nature due to the gravity of
Neptune. The strong influence of Neptune perturbs the orbits of some of these objects and may send them into
new orbits aimed at the inner solar system. When this happens, an object is likely to become a short period
comet. There are many discovered scattered disk objects. The most notable one is Eris, the largest known
scattered disk object to date. Classified as a dwarf planet, Eris is actually bigger than Pluto.
Oort cloud objects are the third category of
Trans-Neptunian object. Oort cloud is believed to have
two parts: the outer spherical cloud, and an inner
disk-like cloud. Oort cloud is huge, it is estimated
to extend to 100,000 AU from the Sun. To put it into
perspective, 200,000 AU is about the distance between
the Sun and Proxima Centauri, our nearest star.
Methane, ammonia, ice are the primary compounds that
make up the Oort cloud objects. Although not directly
observable, Oort cloud’s hypothetical existence would
explain the origin of an isotropic long-period comet.
Famed comet Hale-Bopp with an orbital period that lasts Depiction of the scale of the Oort Cloud, compared to Kuiper Belt
thousands of years is thought to originate from the
Oort cloud. Because the cloud is so far away from the Sun, it is only loosely tied to the Sun’s gravitational
influence. Any interstellar perturbation can disturb the orbits of objects in the Oort cloud and send them toward
the inner solar system or eject them into the nether realms of interstellar space. Spacecrafts like Voyager 1,2
and eventually New Horizons are expected to continue the investigation of this mysterious cloud. (wikipedia)
● News from Mars: Existence of Water, Reason
Behind the Declining Atmosphere
NASA has confirmed the existence of liquid flowing water on Mars, with the help of an imaging
spectrometer on Mars Reconnaissance Orbiter (MRO). Using that
equipment, scientists were able to find evidence that points to the
presence of hydrated minerals on slopes. These slopes were previously
seen with unexplained streaks on them. The streaks with rather a
darkish hue have seemingly shown signs of flowing. During warmer
seasons of the Red Planet, they darkened and flew down slopes.
During colder climate, these streaks faded away. These streaks have
been spotted in multiple locations on Mars, typically when the
temperature was above 10 degrees Fahrenheit. Pure liquid water
cannot sustain its form on such low temperature. The finding points to
the speculation that flowing water on Mars may come with a heavy
dose of minerals dissolved in them. ”the detection of hydrated salts on
The red planet, Mars (NASA.gov)
these slopes means that water plays a vital role in the formation of
these streaks," said Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, lead
author of a report on these findings published Sept. 28 by Nature Geoscience. (NASA.gov)
It has long been estimated that the atmosphere on Mars was slowly stripped away. This has recently
been confirmed by NASA. In addition, the scientists at NASA have attributed this phenomenon to the solar
wind. The results of observation by NASA’s Mars Atmosphere and Volatile Evolution mission (MAVEN) have
confirmed that Mars atmosphere, which is about 96% carbon dioxide, was, and still is, steadily eroded away
by incoming bombardment of charged particles in the solar wind. Unlike the Earth, Mars does not have a
global magnetic field strong enough to shield itself from these charged particles. The erosion process was
likely to be more rapid during early days of the solar system when the Sun was young and much more
volatile. (NASA.gov)
This month in horoscopes: For the month of November, the alignment of the stars suggests that if you are a Sagittarius,
don't even go outside. All month. (Nick Anderson)
Astronomy Club of Virginia Tech, 2015, all rights reserved
Chief Editor: Han Chen [email protected] @Dr_Chen_XRay
Contributors: Nick Anderson