Earth Distance Research Articles

Planet heating prevents inward migration of planetary cores.

Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disk. Concurrently, tidal effects in the disk cause a radial drift in the embryo orbits, a process known as migration. Fast inward migration is predicted by theory for embryos smaller than three to five Earth masses. With only inward migration, these embryos can only rarely become giant planets located at Earth's distance from the Sun and beyond, in contrast with observations. Here we report that asymmetries in the temperature rise associated with accreting infalling material produce a force (which gives rise to an effect that we call 'heating torque') that counteracts inward migration. This provides a channel for the formation of giant planets and also explains the strong planet-metallicity correlation found between the incidence of giant planets and the heavy-element abundance of the host stars.

Astronomical Misconceptions

Do you think that the Moon does not rotate? Do you think that the phases of the Moon are created by the Earth's shadow? Do you think that the seasons are a result of the Earth's distance from the Sun? If you answered “yes” to any of these, then you are one of many who possess misconceptions about astronomy.

Testing regional vertical total electron content maps over Europe during the 17–21 January 2005 sudden space weather event

The intense level of solar activity recorded from 16 to 23 January 2005 led to a series of events with different signatures at the Earth's ionospheric distances. Measurements of the critical frequency of the F2 layer foF2 and the vertical total electron content (VTEC) are used to describe the temporal and spatial electron density distributions during this space weather event, which gives an excellent opportunity to test regional VTEC maps over Europe under such disturbed solar‐terrestrial conditions. In this context, the tests used to validate the International GNSS Service (IGS) VTEC maps have been applied to assess the accuracy of the European Rutherford Appleton Laboratory (RAL) VTEC maps. Thus the self‐consistency test and the Jason altimeter test have been used to compare such performances with the IGS and Universitat Politecnica de Catalunya global ionospheric maps. The results show discrepancies between the RAL maps and the IGS ones, which leads to significant RMS and bias values of several total electron content units. Moreover, in this work a kriging technique to improve the accuracy of any regional VTEC map is also considered, with relative improvements of the RAL VTEC maps up to more than 20% at the peak of the storm.

Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing

Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun.

Emerging Conceptual Understanding of Complex Astronomical Phenomena by Using a Virtual Solar System

This study describes high school students' conceptual development of the basic astronomical phenomena during real-time interactions with a Virtual Solar System (VSS). The VSS is a non-immersive virtual environment which has a dynamic frame of reference that can be altered by the user. Ten 10th grade students were given tasks containing a set of observe–explain questions without mentoring. The findings showed that all participants used the VSS as a visual thinking tool and developed a scientific understanding of the causes of the day–night phenomena. However, alternative dynamic misconceptions of the Earth–Moon–Sun system emerged as a result of (1) cognitive difficulty in coordinating visual information from different perspectives; (2) misinterpreting salient features of the VSS visual representation; (3) ignoring the 3D nature of the Moon's relative motion, together with incorrect perception of the Moon's and the Earth's relative size and distance; and (4) the inability to mentally shift away from the Earth's frame of reference. These findings have significant bearing on our understanding of the educational potential and possible pitfalls of learning via virtual reality environments. The learning should be accompanied by suitable scaffolding and guided reflection to minimize the emergence of alternative astronomical conceptions. Designing additional navigation tools would empower the learners' perceptual and cognitive system.

Lasting effects of instruction guided by the conflict map: Experimental study of learning about the causes of the seasons

This study was based on the framework of the “conflict map” to facilitate student conceptual learning about causes of the seasons. Instruction guided by the conflict map emphasizes not only the use of discrepant events, but also the resolution of conflict between students' alternative conceptions and scientific conceptions, using critical events or explanations and relevant perceptions and conceptions that explicate the scientific conceptions. Two ninth grade science classes in Taiwan participated in this quasi-experimental study in which one class was assigned to a traditional teaching group and the other class was assigned to a conflict map instruction treatment. Students' ideas were gathered through three interviews: the first was conducted 1 week after the instruction; the second 2 months afterward; and the third at 8 months after the treatment. Through an analysis of students' interview responses, it was revealed that many students, even after instruction, had a common alternative conception that seasons were determined by the earth's distance to the sun. However, the instruction guided by the framework of the conflict map was shown to be a potential way of changing the alternative conception and acquiring scientific understandings, especially in light of long-term observations. A detailed analysis of students' ideas across the interviews also strongly suggests that researchers as well as practicing teachers need to pay particular attention to those students who can simply recall the scientific fact without deep thinking, as these students may learn science through rote memorization and soon regress to alternative conceptions after science instruction. © 2005 Wiley Periodicals, Inc. J Res Sci Teach 42: 1089–1111, 2005

Solar neutrinos in Super-Kamiokande-I

Results from the entire 1496 live days of solar neutrino data from Super-Kamiokande-I's 1996–2001 run are presented. These results include our measurements of the Sun's absolute Boron-8 neutrino flux and energy spectrum, as well as studies of their variation with respect to the solar zenith angle (day/night asymmetry) and Earth's distance to the Sun. The possibility of neutrino oscillations is discussed in light of these results and those of other experiments, and the MSW Large Mixing Angle solution is found to be strongly favored.

Some Polarity Conditions in Corpuscular Events

We present some refinements of the previously reported magnetic polarity conditions in solar-terrestrial relations. Appropriately selected subsets were used from the longest available data sets, the geomagnetic aa-index and the surface air temperature. The solar corpuscular impacts have conspicuous effects in the tropospheric behaviour. We reported previously a new kind of semi-annual fluctuation and opposite tropospheric responses to the effects coming from different regions of the Sun as well as their dependence on the orientation of the solar main magnetic dipole. It is shown in the present paper that the semi-annual fluctuation governed by shock and fluctuating disturbances (which originate from the lower-latitude solar regions) exhibits sign reversals in consecutive cycles. The effect can be detected only in the absence of recurrent disturbances (coming mainly from the polar regions). This complex phenomenon implies that the corpuscular events may preserve some of their polarity conditions of their specific solar origin even at the Earth's distance, and on the other hand the small-scale structure of the IMF plays an important role in the link between the solar particles and the tropospheric response.

Occurrence of Earth-Like Bodies in Planetary Systems

Present theories of terrestrial planet formation predict the rapid ;;runaway formation'' of planetary embryos. The sizes of the embryos increase with heliocentric distance. These embryos then merge to form planets. In earlier Monte Carlo simulations of the merger of these embryos it was assumed that embryos did not form in the asteroid belt, but this assumption may not be valid. Simulations in which runaways were allowed to form in the asteroid belt show that, although the initial distributions of mass, energy, and angular momentum are different from those observed today, during the growth of the planets these distributions spontaneously evolve toward those observed, simply as a result of known solar system processes. Even when a large planet analogous to ;;Jupiter'' does not form, an Earth-sized planet is almost always found near Earth's heliocentric distance. These results suggest that occurrence of Earth-like planets may be a common feature of planetary systems.

A cause of the solar wind speed variations: An update

The relation between the solar wind speed (V) observed at the earth's distance and the latitudinal angular distance of the earth (λ) from the magnetic neutral line on the so‐called “source surface” of the sun, which is determined from the spherical harmonic analysis of the line‐of‐sight component of the photospheric magnetic field [Hoeksema et al., 1982], is examined. It is shown that the solar wind speed V increases as |λ| increases and that V does not depend on the heliographic latitude of the earth. This relation may be represented by V(km/s) = 408 + 473sin²λ during the period between May 1976 and August 1977. The presence of such a latitudinal gradient of V indicates that some of the time variations of V observed at the earth are caused by the spatial variations of V with respect to λ.

Flight Luck, and: Lighting The Dark Side of the Moon

FLIGHT LUCK / Cathryn Hankla Apollo 13, can you hear us, this is Houston, the future home of the Astros, in the fisheye of mission control. We are burning with reflections of your three friends who were fired in the multi-billion dollar kiln—one hell of a spectacle. You see, this is Houston, it was nonmetallic material that time, in a pure environment of oxygen, a tiny spark, but we've fixed that now. Galileo, in 1610, invented a way to the moon; he drew his own conclusions, sketched mare in charcoal that still compares to photographs. Sunspots incised twin images of stars on the retinas of his eyes. The telescopic limbs of light went out for him one night. "Houston," we hear you calling, "We've had a problem." But we thought we had that solved, that's why we were dying to defy the laws of luck, launch you charmed at 1313 hours (someone's idea of a joke) on the eleventh day of the fourth month. In just two days, it would occur to us we might have made our second fatal gaffe in much the same manner as our first. This time, again, it was oxygen. A tank burst. When we sent the Ape, Ham, up, no one watched, we never worried how to coach him down to earth. Apollo crew, if you are orbitting, reroute the poison gas, conserve water, there are no lakes in space, alas; eat light, use your waste for ballast, and perhaps, there's a chance, you will have enough breath to see your flight back to us. Good Luck. 16 · The Missouri Review LIGHTING THE DARK SIDE OF THE MOON / Cathryn Hankla "We'll see you on the other side," beamed Lovell before he saw for the first time the far side of the moon. It was Christmas Eve, sixty miles out, and for thirty-four minutes Apollo 8 occulted. The sphere, newsprint adrift in a sea of stars, papier-mâché, or a gray beach mound, felt the scorch of jets. Once it was sound, the ship flawless in orbit, TV sets tuned the blue Earthrise, a mirage of living water on a slide, witnessed from the banks of the moon. Earth's turquoise islands sparked cislunar distance, the astronauts listened to the diamond stylus, to rhythmic seas inside their dreams, as if shells crusted their ears like the curves of space. In that glimpse of the stillborn planet, the astronauts, like Arabian sheikhs, pitched their tent of night; they logged the primeval homesickness, would sleep fitful for a world of color. "In the beginning," began Anders, "God created the heaven and the earth. And the earth was without form. . . ." Lovell said, "Let there be light. . . ." Borman finished, "God saw that it was good." The Missouri Review · 17 ...

A cause of solar wind speed variations observed at 1 A.U.

An attempt is made to interpret solar wind variations observed at the earth's distance, namely the solar cycle variations, the semi‐annual variations, and the 27‐day variations, as well as the polarity changes of the interplanetary magnetic field, mainly in terms of two effects, a positive latitudinal gradient of the solar wind speed and a wobbling solar dipole, combined with the annual (heliospheric) latitudinal excursion of the earth. It is shown that a significant part of the solar wind variations observed at the earth's distance and the changes of polarity pattern of the interplanetary magnetic field can be reasonably well reproduced by the two effects.

Radial deformation of the solar current sheet as a cause of geomagnetic storms

It is suggested that the solar current sheet, extending from a coronal streamer, develops a large-scale radial deformation, at times with a very steep gradient at the Earth's distance. The associated magnetic field lines (namely, the interplanetary magnetic field (IMF) lines) are expected to have also a large gradient in the vicinity of the current sheet. It is also suggested that some of the major geomagnetic storms occur when the Earth is located in the region where IMF field lines have a large dip angle with respect to the ecliptic plane for an extended period (6–48 h), as a result of a steep radial deformation of the current sheet.

Earth and Venus: A comparative study

The observed density of Venus is about 2% smaller than would be expected if Venus were a twin planet of the Earth, possessing an identical internal composition and structure. In principle, this could be explained by a process of physical segregation of metal particles from silicate particles in the solar nebula prior to accretion, so that Venus accreted from relatively metal-depleted material. However, this model encounters severe difficulties in explaining the nature of the physical segregation process and also the detailed chemical composition of the Earth's mantle. Two alternative hypotheses are examined, both of which attempt to explain the density difference in terms of chemical fractionation processes. Both of these hypotheses assume that the relative abundances of the major elements Fe, Si, Mg, Al, and Ca are similar in both planets. According to the first hypothesis, a larger proportion of the total iron in Venus is present as iron oxide in the mantle, so that the core-to-mantle ratio is smaller than in the Earth. This model implies that Venus is more oxidized than the Earth, with its lower intrinsic density (i.e., corrected to equivalent pressures and temperatures) due to the larger amount of oxygen present. The difference between oxidation states is attributed to differing degrees of accretional heating arising from the relatively smaller mass of Venus. On the other hand, the second hypothesis maintains that Venus is more reduced than the Earth, with its mantle essentially devoid of oxidized iron. The difference intrinsic densities is attributed to the Earth accreting at a lower temperature than Venus as a result of the Earth's greater distance from the center of the nebula. As a result, large amounts of sulfur accreted on the Earth but not on Venus. The sulfur, which entered the core, is believed to have increased the mean density of the Earth because of its relatively high atomic weight. The hypothesis also implies that most of the Earth's potassium, because of its chalcophile properties, entered the core.These hypotheses are evaluated in the light of existing data. The second hypothesis leads to an intrinsic density for Venus which is only 0.4% smaller than that of the Earth. This difference is much smaller than is believed to exist. A wide range of chemical evidence is found to be unfavorable to this second hypothesis, but to be consistent with the interpretation that Venus is more oxidized than the Earth, as required by the first hypothesis.

Mars Bright in October Skies

Mars, now making its closest approach to earth since the summer of 1971, will be one of the three bright planets in the October evening skies. On Oct. 16 it will be 40.5 million miles away. It is high in the east in Aries. Mars will shine more brightly than any other planet except Venus, which you can see low in the west soon after sunset. Venus, more than four times as bright as Mars, sets about two hours after the sun, too early to be shown on the above maps (except that its Oct. 31 position is indicated). Jupiter, only slightly fainter, is in the southwest, in Capricornus. Less than a year ago Mars was visible low in the east before dawn, about as bright as the polestar. About Oct. 24 it will be 50 times brighter than it was then. Among the planets only Venus can become brighter. In succeeding months Mars will fade, then brighten again during 1975. By December 1975 it will once more be prominent, although only about half as brilliant as now. In January 1978, it will shine with about two-thirds of its 1975 brilliance. It will again be on view in February 1980 and still fainter. But even then it will be more brilliant than any of the stars around it except Sirius (the star in Canis Major, which is so conspicuous on winter evenings). On following returns, in 1982, 1984 and 1986, Mars will be successively brighter. By September 1988, it will be even more prominent than now although fainter than in August 1971. The reason for these wide variations in brightness is the considerable eccentricity of Mars' orbit. It departs from a perfect circle more than any other planet except Pluto and Mercury. Earth's mean distance from the sun is 93 million miles; that of Mars 141.7 million. We encircle the sun every 12 months while Mars goes around in about 22.5 months. Every 2 years and 2 months earth catches up to Mars and Mars is closest to us. This is called an opposition because Mars is directly opposite the sun. This year, on Oct. 16, Mars will be 40,532,000 miles from earth. Mars will be more than 5 million miles farther than it was in 1971, but it will be higher in the sky for Northern Hemisphere observers and thus more easily seen. The closest approaches always occur in August, when Mars is far south. The above maps show the skies as they look on Oct. I about 11 p.m., local daylight saving time; 10 p.m. on the 15th, and 8 p.m. standard time to which we will return on Sunday, Oct. 28. l

Temperatures of meteoroids and meteorites

The effects of emissivity, absorptivity, and thermal inertia are taken into account in the calculation of meteoroid temperatures at the earth's distance from the sun. Iron meteoroids at 1 AU with equivalent sphere radii in excess of about 1.5 meters may have temperatures departing substantially from radiative equilibrium temperatures as they move toward or away from the sun in highly eccentric orbits. The radiative equilibrium temperature of stone meteoroids is less than 0°C, whereas for iron meteoroids, it is substantially greater than 0°C. These results are consistent with observed temperatures of newly fallen meteorites.

Temperature models for the outer solar atmosphere

A reexamination of “observed” electron densities in the solar corona and corona extended, plus Explorer X data shows that an inverse square law for the density variation is a good approximation. Such as law implies a constantly expanding model for the solar corona. An analytical expression is obtained for the temperature profile using this model. Without adjusting any constants, one obtains a temperature of 3500° K at 0.00025 solar radii above the limb, a maximum temperature of 1.65 × 10 6 °K at 0.7 solar radii and 2.16 × 10 4 °K at the Earth's orbital distance. This temperature distribution is compared with one based on modifications of the hydrostatic model of Pottasch; a close agreement is found (Table I). The consequences of this agreement are discussed.

Temperature Models for the Outer Solar Atmosphere.

Abstract A reexamination of “observed” electron densities in the solar corona and corona extended, plus Explorer X data shows that an inverse square law for the density variation is a good approximation. Such as law implies a constantly expanding model for the solar corona. An analytical expression is obtained for the temperature profile using this model. Without adjusting any constants, one obtains a temperature of 3500° K at 0.00025 solar radii above the limb, a maximum temperature of 1.65 × 10 6 °K at 0.7 solar radii and 2.16 × 10 4 °K at the Earth's orbital distance. This temperature distribution is compared with one based on modifications of the hydrostatic model of Pottasch; a close agreement is found (Table I). The consequences of this agreement are discussed.

Light scattering by small particles in the zodiacal cloud

view Abstract Citations (15) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Light scattering by small particles in the zodiacal cloud Little, S. J. ; O'Mara, B. J. ; Aller, L. H. Abstract Models of the zodiacal cloud in the plane of the ecliptic have been computed using scattering functions taken from experimental results of Richter et al. (1962 a) and the Mie theory for spherical particles. We have attempted to determine the size distribution, the density variation, the number density at the earth's distance, the albedo, and the composition (dielectric versus metallic particles). We have compared Richter's results with those predicted for the same particle size distribution to assess whether it is justifiable to apply the Mie theory for crushed nonspherical aggregates. The existing zodiacal light observations permit a wide range of solution in particle size distribution, density distribution, etc., for plausible choices of dielectric materials. It is probable that the metallic component is small. The contribution of electrons to the brightness and polarization of the zodiacal cloud must be very small, indeed. Publication: The Astronomical Journal Pub Date: June 1965 DOI: 10.1086/109746 Bibcode: 1965AJ.....70..346L full text sources ADS |

The neutral hydrogen flux in the solar plasma flow—I

It is shown that the photo-ionization by the extreme ultraviolet radiation of the Sun is not likely to change seriously the initial degree of ionization ( x 1, see sections 4 and 5) of the chromospheric plasma during its passage to the Earth's distance. Thus, the plasma ejected from an active region of the Sun can contain an appreciable amount of neutral hydrogen atoms. The development of the main phase of geomagnetic storms and the formation of the ring current belt by such an incompletely ionized solar plasma are discussed.