The Sun is a wondrous beacon. It is the primary energy source that drives so many Earth systems. But how much do scientists know about its energy output and the variance of this output? Research into this area has tangible ramifications for life on Earth.
Astrobiology is often concerned with mysteries of the past: Researchers vigorously pursue questions such as, “How did life on Earth originate,” “What was its course of evolution,” and “Did life originate elsewhere?” However, equally important are the questions that address the future. We are especially curious about Earth’s future, as well as humankind’s future off this planet. But to learn more about the prospects for our planet, we must understand the near and long term changes in Earth’s space environment.
This two part series will delve into the research involving our Sun, and how even slight energy variation can induce larger-scale changes on Earth. This installment will focus on what we know about our Sun and the current efforts to understand more about its periodic fluctuations. Part II will get into more of the astrobiological effects of how the Sun influences our climate, technology, and space missions.
At Home with our Star
The sun is a very dynamic body. More dramatically, we see changes in solar flares and prominences emanating from its surface. Scientists also monitor an eleven-year periodicity of the Sun by tracing the movement of Sunspots. But the dynamic nature of our star has consequences that are not limited to the space near the Sun: Earth frequently encounters varying levels of radiation (energy in the form of electromagnetic waves) and solar wind. The ramifications of this variation are not entirely clear. Thus, researchers continue to deploy solar monitoring satellites to get a better understanding of our star.
The following sections provide a brief summary of some of the spacecraft that study the Sun. A much more comprehensive list is available at the Sun-Earth Connection Missions website at Goddard Space Flight Center.
Early and Recent Monitoring Efforts
The atmosphere is a protective blanket that surrounds Earth. Without it, our planet would be pelted by an entire spectrum of intense, harmful radiation. But this protective layer also prohibits us from accurately measuring solar output. Thus, to get a true understanding of Sun-Earth interactions, scientists must study the Sun from space.
The history of solar missions is as old as the space age itself. Explorer 1, the first U.S. satellite, studied the radiation belts that surround Earth in 1958. Later, Skylab missions (1970s) investigated the corona and other aspects of the Sun. Following these earlier efforts, there has been a cadre of spacecraft aimed at increasing our understanding solar variance, energetic output, and Sun-Earth interaction.
One of theses solar missions is the Active Cavity Radiometer Irradiance Monitor Satellite (ACRIMSAT). ACRIM instrumentation has more than a 20-year history of solar exploration. There have been three instrument packages to carry the ACRIM name. ACRIM I, launched in 1980, was the first to clearly demonstrate that total radiant energy from the Sun is not constant. This is perhaps one of the most important insights gained from this type of study. Before this time, scientists assumed that the solar constant did not change much during a human lifetime. ACRIMSAT, which carries ACRIM III, was launched in 1999 and is currently on a five-year mission to measure Total Solar Irradiance (TSI) .
Studying the Sun-Earth Connection
NASA’s most recent addition to solar monitoring spacecraft, Solar Radiation and Climate Experiment (SORCE), was launched successfully on January 25, 2003. SORCE has state-of-the-art radiometers, spectrometers, and photodiodes that will be monitoring incoming x-ray, ultraviolet, near-infrared, and total solar radiation. SORCE is one of the first missions specifically designed with questions like “What role does the Sun play in our climate and how do changes within the Sun affect us?” This interrelation between Sun and Earth climate is a paramount question when dealing with questions about near and long-term global change. You can learn more about this mission by going to University of Colorado’s (the lead team) SORCE homepage.
The next generation of solar exploration is NASA’s “Living with a Star” (LWS) program. LWS has two major groups of missions: the solar dynamics element, to be served by Solar Dynamics Sentinels, and the geospace dynamics elements, to be served by the Geospace Missions Network. Over the 11-year solar cycle, LWS will help quantify the dynamics and behavior of the Sun-Earth system. Specifically, it seeks to improve our understanding of solar variability and the resulting Earth systems disturbances. Through LWS spacecraft, scientists hope to have a better understanding of space weather, and thus develop a more predictive capability of the changes that can occur in the space environment (to be discussed more in Part II). For more on Living with a Star, you can visit the homepage at Goddard Space Flight Center: http://lws.gsfc.nasa.gov/.
In Part II, we will expand upon what we’ve learned about the Sun and the current missions that are aimed at understanding solar variation. “Effects on Earth” will go one step further in elucidating possible near term consequences of living with an energetic, sometimes unpredictable star. Most importantly, we will return to the important astrobiological question, “What is life’s future on Earth and beyond.”