16 research outputs found
Populations of planets in multiple star systems
Astronomers have discovered that both planets and binaries are abundant
throughout the Galaxy. In combination, we know of over 100 planets in binary
and higher-order multi-star systems, in both circumbinary and circumstellar
configurations. In this chapter we review these findings and some of their
implications for the formation of both stars and planets. Most of the planets
found have been circumstellar, where there is seemingly a ruinous influence of
the second star if sufficiently close (<50 AU). Hosts of hot Jupiters have been
a particularly popular target for binary star studies, showing an enhanced rate
of stellar multiplicity for moderately wide binaries (>100 AU). This was
thought to be a sign of Kozai-Lidov migration, however recent studies have
shown this mechanism to be too inefficient to account for the majority of hot
Jupiters. A couple of dozen circumbinary planets have been proposed around both
main sequence and evolved binaries. Around main sequence binaries there are
preliminary indications that the frequency of gas giants is as high as those
around single stars. There is however a conspicuous absence of circumbinary
planets around the tightest main sequence binaries with periods of just a few
days, suggesting a unique, more disruptive formation history of such close
stellar pairs.Comment: Invited review chapter, accepted for publication in "Handbook of
Exoplanets", ed. H. Deeg & J. A. Belmont
Recent Arctic amplification and extreme mid-latitude weather
The Arctic region has warmed more than twice as fast as the global average — a phenomenon known as Arctic amplification. The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover, at a pace greater than that simulated by climate models. These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes, including severe winters. The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation. Through changes in these key atmospheric features, it is possible, in principle, for sea ice and snow cover to jointly influence mid-latitude weather. However, because of incomplete knowledge of how high-latitude climate change influences these phenomena, combined with sparse and short data records, and imperfect models, large uncertainties regarding the magnitude of such an influence remain. We conclude that improved process understanding, sustained and additional Arctic observations, and better coordinated modelling studies will be needed to advance our understanding of the influences on mid-latitude weather and extreme events
Snow in the changing sea-ice systems
Snow is the most reflective, and also the most insulative, natural material on Earth. Consequently, it is an integral part of the sea-ice and climate systems. However, the spatial and temporal heterogeneities of snow pose challenges for observing, understanding and modelling those systems under anthropogenic warming. Here, we survey the snow–ice system, then provide recommendations for overcoming present challenges. These include: collecting process-oriented observations for model diagnostics and understanding snow–ice feedbacks, and improving our remote sensing capabilities of snow for monitoring large-scale changes in snow on sea ice. These efforts could be achieved through stronger coordination between the observational, remote sensing and modelling communities, and would pay dividends through distinct improvements in predictions of polar environments