PATHWAYS TO
DISCOVERY

The program laid out in this report represents a collective vision for the future and will require the engagement of a broad community to advance.

A decadal survey not only captures a vision of what we may achieve but also charts a clear path to achieving it. What investments are needed today to lay the groundwork for ambitious future missions? How can we reap the greatest benefit from past investments and current endeavors? How can we craft programs that are responsive to evolving scientific knowledge and poised to take advantage of future technological advancements?

Enabling breakthroughs in priority scientific areas requires a range of strategic investments at multiple scales. It requires space-based missions that will venture far from Earth to bring a profoundly new perspective on our place in the universe. It requires ground-based initiatives that will probe new facets of physics and observe the universe with unprecedented sensitivity. And it requires comprehensive strategies to support the field’s foundations by investing in the people who drive innovation and the facilities and technologies that enable the science.

We are poised to tackle some questions that are so grand that the facilities and instruments needed to address them require vision and commitments that span generations and borders. To realize the bold vision outlined in this decadal survey requires a re-imagining of the ways in which large missions are developed and implemented. While the substantial cost of envisioned missions likely limits the ability to pursue all of the worthy ideas simultaneously, setting priorities among those ideas, based on the scientific opportunities they present, can help us to maximize the return on investment. With more early investments in co-maturing mission concepts and technologies, with room for checks and course corrections along the way, and with a workforce that utilizes the broadest range of human talent, we can achieve incredible scientific gains.

Space-Based Initiatives

Since its founding, the National Aeronautics and Space Administration (NASA) has pioneered audacious, far-reaching missions to explore the cosmos from space. Taking advantage of the extreme conditions of space and unique vantage points not attainable anywhere on Earth, these programs have dramatically expanded scientific knowledge and positioned the United States as a global leader in astronomy and astrophysics.

The next decade and beyond presents opportunities to build on these successes and extend our knowledge into the next frontiers. A suite of overlapping missions to observe the universe using multiple wavelengths will provide the different and complementary views of the cosmos required to address the full set of Astro2020 scientific objectives.

A New Approach for a New Generation of Space Telescopes

To enable the strategic missions envisioned for the

coming decades, the decadal survey recommends a new approach to co-developing the science, mission architectures, and technologies for space telescopes. A Great Observatories Mission and Technology Maturation Program would guide the maturation and provide checks to adjust the course along the way in order to ensure consistency with the recommended cost and schedule targets.

Top Priorities for Large Space-Based Initiatives

Key priorities recommended for a Great Observatories Mission and Technology Maturation Program include an infrared/optical/ultraviolet (IR/O/UV) space observatory, a far-infrared spectroscopy and imaging mission, and a high spatial resolution X-ray strategic mission.

A large IR/O/UV space telescope designed to search for life on other planets is the priority to enter the maturation program first. This flagship mission would combine high-contrast imaging (capable of observing planets 10 billion times fainter than their star) with spectroscopic capabilities covering near-infrared, visible, and ultraviolet wavelengths to study the atmospheres of Earth-like, habitable-zone planets, and it would be transformative for general astrophysics.

Other high priorities include

• An astrophysics probe-class mission program, with recommended initial projects including a far-infrared spectroscopy or imaging mission to provide broad wavelength coverage and scientific balance and an X-ray probe to investigate highly energetic phenomena
• A time-domain and multi-messenger program of small- and medium-scale missions to sustain space-based, electromagnetic capabilities for studying transient phenomena, such as those discovered via gravitational waves and neutrinos

Ground-Based Initiatives

Recent years have seen exceptional innovation and global collaboration in ground-based infrastructure for astronomy and astrophysics research, pushing the boundaries of our observational capabilities to elucidate the fundamental physical processes of our universe.

Ground-based instruments offer numerous benefits—avoiding the operational constraints of space, they can be constructed and maintained in place, often allowing them to be used by a broader community of scientists and for a broader array of purposes. With their support for a wide range of ground-based initiatives, the National Science Foundation (NSF) and the U.S. Department of Energy (DOE) put U.S. scientists at the forefront of discovery and uphold our nation’s tradition as a key partner in global-scale scientific initiatives.

Top Priorities for Large Ground-Based Initiatives

Advancing a coordinated U.S. Extremely Large Telescope (ELT) program is the top priority for ground-based initiatives in the coming decade. Two ELTs, the Giant Magellan Telescope and the Thirty Meter Telescope—already well into development and expected to commence operations in the mid-2030s, contingent on a U.S. funding commitment—will offer a powerful combination of capabilities that can be brought to bear on nearly all of the high-priority scientific questions envisioned for the coming decade. The decadal survey recommends investing in at least one of the two ELTs, but a two-telescope program is strongly preferred because it offers the advantage of full-sky coverage and maximizes the amount of observing time accessible to U.S. researchers.

Other high priorities include

• Cosmic Microwave Background Stage 4 (CMB-S4) observatory to trace feedbacks within cosmic ecosystems and search for signals from the Big Bang
• Next Generation Very Large Array (ngVLA) to replace the two existing large radio telescope arrays while improving sensitivity by roughly an order of magnitude

Key Recommendations for Ground-Based Initiatives

Supporting the Foundations of Astronomy and Astrophysics

Realizing the full potential of a new generation of space- and ground-based initiatives requires a robust foundation of expertise, technology, and research infrastructure. The decadal survey outlines key actions needed to address gaps, ensure accountability, speed scientific advances, and strengthen the overall U.S. astronomy and astrophysics pipeline in accordance with our nation’s values and aspirations.

Driving Innovation

People are the most fundamental component of the research enterprise; human creativity and innovative capacity are vital to transforming data into understanding and discovery. Science is at its most innovative only when it maximizes and fully utilizes the diversity of human talent. In addition, equity demands that scientific endeavors pursued with the nation’s resources are done in a manner consistent with the principles of fairness and equal opportunity that are core to society’s ideals.

Anyone with the ability and the drive to contribute to scientific discovery should have a fair chance to do so, and be free of fear, harassment, or discrimination. The decadal survey recommends programs to support the scientific workforce, in particular early-career researchers, with a strong emphasis on broadening access, removing barriers to participation, and fostering a safe and inclusive professional environment.

The pursuit of science and scientific excellence is inseparable from the humans who animate it.

Sustaining the Engines of Discovery

Tools, technologies, and research coordination are essential to scientific progress. To maximize the utility of scientific resources, it is critical to adequately support the costs of developing, operating, and maintaining state-of-the-art instruments and facilities. To get the greatest possible value out of the data generated, it is vital to adequately support archives, data pipelines, laboratory work, and theoretical tools that provide the cross-cutting foundations for discovery.

Recommendations for Supporting the Foundations for the Profession

Recommendations for Supporting the Foundations for Research

Recommendations for Supporting the Foundations for Technology